Barometric pressure correction based on remote sources of information

ABSTRACT

The invention includes systems and methods for converting absolute pressure data acquired in anatomical environments to gauge pressure data using an implant configured to monitor pressure. The implant is configured to communicate with an external controller, which is configured to communicate with a remote microprocessor that includes real-time barometric pressure data for one or more geographic locations.

RELATED APPLICATION DATA

[0001] This is a continuation-in-part of U.S. application Ser. No.09/989,912, filed Nov. 19, 2001, which is a continuation-in-part of U.S.application Ser. No. 09/690,615, Filed Oct. 16, 2000. This is also acontinuation-in-part of U.S. application Ser. No. 09/888,272, filed Jun.21, 2001, which is a continuation-in-part of U.S. application Ser. No.09/690,615, filed Oct. 16, 2000. The aforementioned applications are allincorporated herein by reference in their entireties.

FIELD OF THE INVENTION

[0002] The present invention relates generally to barometric pressurecorrection in implantable biosensors, and more particularly tobarometric pressure correction for implantable pressure sensors based onremote sources of information, including remote databases and web sites.

BACKGROUND OF THE INVENTION

[0003] Devices are known that may be implanted within a patient's bodyfor monitoring one or more physiological conditions and/or to providetherapeutic functions. For example, sensors or transducers may belocated deep within the body for monitoring a variety of properties,such as temperature, pressure, strain, fluid flow, chemical properties,electrical properties, magnetic properties, and the like. In addition,devices may be implanted that perform one or more therapeutic functions,such as drug delivery, defibrillation, electrical stimulation, and thelike.

[0004] Often it is desirable to communicate with such devices once theyare implanted within a patient using an external controller, forexample, to obtain data, and/or to activate or otherwise control theimplant. An implant may include wire leads from the implant to anexterior surface of the patient, thereby allowing an external controlleror other device to be directly coupled to the implant. Alternatively,the implant may be remotely controlled, e.g., using an externalinduction device. For example, an external radio frequency (RF)transmitter may be used to communicate with the implant. RF energy,however, may only penetrate a few millimeters into a body, because ofthe body's dielectric nature, and therefore may not be able tocommunicate effectively with an implant that is located deep within thebody. In addition, although an RF transmitter may be able to induce acurrent within an implant, the implant's receiving antenna, generally alow impedance coil, may generate a voltage that is too low to provide areliable switching mechanism.

[0005] In a further alternative, electromagnetic energy may be used tocontrol an implant, since a body generally does not attenuate magneticfields. The presence of external magnetic fields encountered by thepatient during normal activity, however, may expose the patient to therisk of false positives, i.e., accidental activation or deactivation ofthe implant. Furthermore, external electromagnetic systems may becumbersome and may not be able to effectively transfer coded informationto an implant.

[0006] Notably, implantable biosensors that measure pressure deep withinanatomical structures such as blood vessels or the brain, can onlycommunicate the absolute pressure associated with the immediateanatomical environment. These devices are not capable of communicatinggauge pressure because they are confined and sealed away from theambient pressure external the body. In most cases, it is gauge pressureand not absolute pressure that is sought to be known, since the bodyregulates its activities based on the ambient pressure. Gauge pressuremay be determined by correlating the absolute pressure with the ambientpressure. For example, Miesel et al. (U.S. Pat. No. 6,248,080), whichisincorporated herein by reference, uses a barometer to determine gaugepressure based on a correlation of absolute pressure and ambientpressure. The Miesel system, however, requires a barometer to determinethe ambient pressure.

SUMMARY OF THE INVENTION

[0007] The invention is generally directed to systems and methods formeasuring pressure in a sealed or isolated system by converting orcorrecting data received from the sealed or otherwise isolated systemusing one or more remote databases. This generally involves a sensorplaced within an isolated or enclosed system. Such enclosed systems caninclude anatomical structures such as blood vessels within a humancirculatory system or other anatomical locations. They can also includeisolated systems associated with automobiles, such as braking systems,cooling systems, cylinders and combustion chambers of an internalcombustion engine, air intake systems, fuel systems includingcarburetors, electrical systems, air conditioning and heating systems,etc. The sensors can include those that are capable of measuringpressure, temperature, electrical impedance, position, strain, pH, fluidflow, chemical properties, electrical properties, magnetic propertiesand the like. An external monitor is used to communicate with theisolated sensor and obtain data about the parameters that are monitoredby the sensor. The communication means can be wireless and can involvethe transmission and reception of any type of telemetric signalincluding acoustic, RF, microwave, electromagnetic, light (e.g.infrared), etc. The external monitor can include one or more transducersto convert the telemetric signal into an electric signal, which can beprocessed by a microprocessor integrated into the external monitor. Theexternal monitor can also include a GPS receiver to communicategeographic location data including altitude data to the microprocessor.The external monitor can communicate through various means known in theart with an external or remote database that includes real-time data,such as real-time temperature or barometric pressure data associatedwith numerous geographic locations. The remote database can beassociated with a web site such as Yahoo® weather, weather.com, AWS.com,etc. The external monitor can use specific information obtained from theremote database to correct data received from the sensor. It can alsouse the real-time data to calibrate a measurement device, such as abarometer, which can be an integrated component of the external monitoror a stand-alone device in communication with the external monitor.

[0008] In one embodiment, the invention is directed to a system formeasuring pressure in a body. The system includes an implant deviceconfigured for measuring absolute pressure in a body. The implant isalso configured to communicate any measured absolute pressureinformation outside of the body using telemetric signals. The systemalso includes an external monitor that is configured to receivetelemetric signals from the implant device. It is also configured toreceive barometric pressure information from a remote source. Thebarometric pressure information can be associated with the geographiclocation of the body. The external monitor is also configured to derivegauge pressure from the received absolute pressure information andbarometric pressure information. The remote source with which theexternal monitor is configured to communicate can be associated with aweb site that includes weather information, such as barometric pressureinformation for numerous locations around the world. The system can alsoinclude a global position system (GPS) signal receiver, which can becoupled either to the implant device or to the external monitor. Thus,both or either the implant device or the external monitor can beconfigured to receive geographic position information from the GPSsignal receiver. The external monitor can be configured to communicatethis position information to the remote source, and to request andreceive barometric pressure information that corresponds with thegeographic position.

[0009] In another embodiment, the invention is directed to a method formeasuring pressure in a body. The method includes receiving a telemetricsignal from a biosensor implanted in a body. The telemetric signal canrepresent absolute pressure information or data. The method alsoincludes receiving real-time barometric pressure information from aremote source, the real-time barometric pressure informationcorresponding to a geographic location of the body. The geographiclocation of the body can be determined in a number of ways includingusing a GPS receiver, a postal code, or a telephone number. Gaugepressure is then derived from the absolute pressure information andbarometric pressure information, and can be displayed on a displayproximate the body, such as on an external monitor or a computermonitor. The gauge pressure can be derived by the external monitor, theimplanted biosensor, or the remote source. The remote source can, forexample, be associated with a web site that includes weather informationsuch as Yahoo® weather, Weather.com, AWS.com, or any other web site thatprovides barometric pressure data for numerous geographic locations.Alternatively, it can be a restricted proprietary database availableonly for the purpose of correcting absolute pressure data.

[0010] Other objects and features of the present invention will becomeapparent from consideration of the following description taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The invention is herein described, by way of example only, withreference to the accompanying drawings, wherein:

[0012] FIGS. 1A-1C are schematic drawings, showing exemplary embodimentsof an implant, in accordance with the present invention.

[0013]FIG. 2 is a schematic of an exemplary circuit for use as anacoustic switch, in accordance with the present invention.

[0014]FIG. 3 is a cross-sectional view of a patient's body, showing asystem for communicating with an implant, in accordance with the presentinvention.

[0015]FIG. 4 is a schematic of an external monitor for communicatingwith an implant, such as that shown in FIG. 3, in accordance with thepresent invention.

[0016]FIG. 5 is a schematic of another exemplary embodiment of animplant, in accordance with the present invention.

[0017]FIG. 6 is a perspective view of an exemplary embodiment of apressure sensing implant, in accordance with the present invention.

[0018]FIG. 7 is a schematic layout of the implant of FIG. 6.

[0019]FIG. 8A is a top view of an energy exchanger that may be providedin an implant, such as that shown in FIGS. 6 and 7, in accordance withthe present invention.

[0020]FIG. 8B is a cross-sectional view of the energy exchanger of FIG.8A, taken along line B-B.

[0021]FIG. 9 is a schematic of an exemplary embodiment of a rectifierfor use with an implant, such as that shown in FIG. 7.

[0022]FIG. 10 is a schematic of another exemplary embodiment of arectifier for use with an implant, such as that shown in FIG. 7.

[0023]FIG. 11 is a schematic of an exemplary embodiment of atransmission circuit for use with an implant, such as that shown in FIG.7.

[0024]FIG. 12 is a schematic of another exemplary embodiment of atransmission circuit for use with an implant, such as that shown in FIG.7.

[0025]FIG. 13A is a top view of an another embodiment of an implant, inaccordance with the present invention.

[0026]FIG. 13B is a side view of the implant of FIG. 13A.

[0027]FIG. 14 is a cross-sectional view of a patient's body, showing anexternal device communicating with an implant located within thepatient's body.

[0028]FIGS. 15A and 15B are diagrams of a barometric pressure correctingsystem in communication with a database having barometric pressure dataaccording to one embodiment.

[0029]FIG. 16 is a block diagram depicting the flow of information in abarometric pressure correcting system according to one embodiment.

[0030]FIG. 17 is a block diagram depicting the flow of information in abarometric pressure correcting system according to another embodiment.

[0031]FIG. 18A is a block diagram depicting the flow of information in abarometric pressure calibration system according to another embodiment.

[0032]FIG. 18B is a block diagram depicting the flow of information in abarometric pressure calibration system according to another embodiment.

[0033]FIG. 19 is a flow chart of some embodiments of methods of thepresent invention.

[0034]FIG. 20 is a flow chart of other embodiments of methods of thepresent invention.

[0035]FIG. 21 is a diagram of a system for delivering barometricpressure information to a medical device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Turning to the drawings, various embodiments of biosensorimplants and external controllers (also referred to as externalmonitors) configured to communicate with biosensor implants are firstshown and described. FIGS. 1A-1C schematically show several exemplaryembodiments of an implant 110, 210, 310, in accordance with the presentinvention. Generally, the implant 110, 210, 310 includes an electricalcircuit 112, 212, 312 configured for performing one or more functions orcommands when the implant 110, 210, 310 is activated, as describedfurther below. In addition, the implant 110, 210, 310 includes an energystorage device 114 and optionally may include a switch 116 coupled tothe electrical circuit 112, 212, 312 and the energy storage device 114.The switch 116 may be activated upon acoustic excitation 100 from anexternal acoustic energy source (not shown) to allow current flow fromthe energy storage device 114 to the electrical circuit 112, 212, 312.

[0037] In one embodiment, the switch 116 includes an acoustic transducer118, such as that disclosed in PCT Publication No. WO 99/34,453,published Jul. 8, 1999, or in U.S. application Ser. No. 09/888,272,filed Jun. 21, 2001, the disclosures of which are expressly incorporatedherein by reference. In addition, the switch 116 also includes a switchcircuit 120, such as switch circuit 400 shown in FIG. 2, althoughalternatively other switches, such as a miniature electromechanicalswitch and the like (not shown) may be provided. In a furtheralternative, the acoustic transducer 118 may be coupled to theelectrical circuit 112, 212, 312 and/or the energy storage device 114,and the switch circuit 120 may be eliminated.

[0038] The energy storage device 114 may be any of a variety of knowndevices, such as an energy exchanger, a battery and/or a capacitor (notshown). Preferably, the energy storage device 114 is capable of storingelectrical energy substantially indefinitely for as long as the acousticswitch 116 remains open, i.e., when the implant 110, 210, 310 is in a“sleep” mode. In addition, the energy storage device 114 may be capableof being charged from an external source, e.g., inductively usingacoustic telemetry, as will be appreciated by those skilled in the art.In an exemplary embodiment, the energy storage device 114 includes botha capacitor and a primary, non-rechargeable battery. Alternatively, theenergy storage device 114 may include a secondary, rechargeable batteryand/or capacitor that may be energized before activation or use of theimplant 110, 210, 310.

[0039] The implant 110, 210, 310 may be surgically or minimallyinvasively inserted within a human body in order to carry out a varietyof monitoring and/or therapeutic functions. For example, the electricalcircuit 112, 212, 312 may include a control circuit 122, 222, 322, abiosensor 124, 224, an actuator 226, 326, and/or a transmitter 128, asexplained in application Ser. No. 09/690,015, incorporated by referenceabove. The implant 210, 310 may be configured for providing one or moretherapeutic functions, for example, to activate and/or control atherapeutic device implanted within a patient's body, such as an atrialdefibrillator or pacemaker, a pain relief stimulator, aneuro-stimulator, a drug delivery device, and/or a light source used forphotodynamic therapy. Alternatively, the implant may be used to monitora radiation dose including ionizing, magnetic and/or acoustic radiation,to monitor flow in a bypass graft, to produce cell oxygenation andmembrane electroporation, and the like. In addition or alternatively,the implant 110 may be used to measure one or more physiologicalparameters within the patient's body, such as pressure, temperature,electrical impedance, position, strain, pH, and the like.

[0040] The implant may operate in one of two modes, a “sleep” or“passive” mode when the implant remains dormant and not in use, i.e.,when the acoustic switch 116 is open, and an “active” mode, when theacoustic switch 116 is closed, and electrical energy is delivered fromthe energy storage device 114 to the electrical circuit 112, 212, 312.Alternatively, the implant may operate continuously or intermittently.Because the acoustic switch 116 is open in the sleep mode, there issubstantially no energy consumption from the energy storage device 114,and consequently, the implant may remain in the sleep mode virtuallyindefinitely, i.e., until activated. Thus, an implant in accordance withthe present invention may be more energy efficient and, therefore, mayrequire a relatively small energy storage device than implants thatcontinuously draw at least a small amount of current in their “passive”mode.

[0041] Turning to FIG. 1A, an exemplary embodiment of an implant 110 isshown in which the electrical circuit 112 includes a control circuit122, a biosensor 124 coupled to the controller 122, and a transmitter128 coupled to the control circuit 122. The controller 122 may includecircuitry for activating or controlling the biosensor 124, for receivingsignals from the biosensor 124, and/or for processing the signals intodata, for example, to be transmitted by the transmitter 128. Optionally,the electrical circuit 112 may include memory (not shown) for storingthe data. The transmitter 128 may be any device capable of transmittingdata from the control circuit 122 to a remote location outside the body,such as an acoustic transmitter, a radio frequency transmitter, and thelike. Preferably, the control circuit 122 is coupled to the acoustictransducer 118 such that the acoustic transducer 118 may be used as atransmitter 128, as well as a receiver, instead of providing a separatetransmitter.

[0042] The biosensor 124 may include one or more sensors capable ofmeasuring physiological parameters, such as pressure, temperature,electrical impedance, position, strain, pH, fluid flow, electrochemicalsensor, and the like. Thus, the biosensor 124 may generate a signalproportional to a physiological parameter that may be processed and/orrelayed by the control circuit 122 to the transmitter 128, which, inturn, may generate a transmission signal to be received by a deviceoutside the patient's body. Data regarding the physiologicalparameter(s) may be transmitted continuously or periodically until theacoustic switch 116 is deactivated, or for a fixed predetermined time,as will be appreciated by those skilled in the art.

[0043] Turning to FIG. 1B, another exemplary embodiment of an implant210 is shown in which the electrical circuit 212 includes a controlcircuit 222 and an actuator 226. The actuator 226 may be coupled to atherapeutic device (not shown) provided in or otherwise coupled to theimplant 210, such as a light source, a nerve stimulator, adefibrillator, an electrochemical oxidation/reduction electrode, or avalve communicating with an implanted drug reservoir (in the implant orotherwise implanted within the body in association with the implant).

[0044] When the switch 120 is closed, the control circuit 222 mayactivate the actuator 226 using a pre-programmed protocol, e.g., tocomplete a predetermined therapeutic procedure, whereupon the switch 120may automatically open, or the controller 222 may follow a continuous orlooped protocol until the switch 120 is deactivated. Alternatively, theacoustic transducer 118 may be coupled to the control circuit 222 forcommunicating a new or unique set of commands to the control circuit222. For example, a particular course of treatment for a patient havingthe implant 210 may be determined, such as a flow rate and duration ofdrug delivery, drug activation, drug production, or an energy level andduration of electrical stimulation. Acoustic signals including commandsspecifying this course of treatment may be transmitted from an externalcontroller (not shown), as described below, to the acoustic switch 116,e.g., along with or subsequent to the activation signal 100. The controlcircuit 222 may interpret these commands and control the actuator 226accordingly to complete the course of treatment.

[0045] Turning to FIG. 1C, yet another exemplary embodiment of animplant 310 is shown in which the electrical circuit 312 includes acontrol circuit 322, a biosensor 324, and an actuator 326, all of whichmay be coupled to one another. This embodiment may operate similarly tothe embodiments described above, e.g., to obtain data regarding one ormore physiological parameters and/or to control a therapeutic device. Inaddition, once activated, the control circuit 322 may control theactuator 326 in response to data obtained from the biosensor 324 tocontrol or adjust automatically a course of treatment being provided bya device connected to the actuator 326. For example, the actuator 326may be coupled to an insulin pump (not shown), and the biosensor 324 maymeasure glucose levels within the patient's body. The control circuit322 may control the actuator to open or close a valve on the insulinpump to adjust a rate of insulin delivery based upon glucose levelsmeasured by the biosensor 324 in order to maintain the patient's glucosewithin a desired range.

[0046] Turning to FIG. 2, an exemplary embodiment of a switch 400 isshown that may be incorporated into an implant in accordance with thepresent invention. The switch 400 includes a piezoelectric transducer,or other acoustic transducer (not shown, but generally connected to theswitch 400 at locations piezo + and piezo -), a plurality of MOSFETtransistors (Q1-Q4) and resistors (R1-R4), and switch S1. A “load” maybe coupled to the switch 400, such as one of the electrical circuitsdescribed above. In the switch's “sleep” mode, all of the MOSFETtransistors (Q1-Q4) are in an off state. To maintain the off state, thegates of the transistors are biased by pull-up and pull-down resistors.The gates of N-channel transistors (Q1, Q3 & Q4) are biased to groundand the gate of P-channel transistor Q2 is biased to +3V. During thisquiescent stage, switch S1 is closed and no current flows through thecircuit. Therefore, although an energy storage device (not shown, butcoupled between the hot post, labeled with an exemplary voltage of +3V,and ground) is connected to the switch 400, no current is being drawntherefrom since all of the transistors are quiescent.

[0047] When the acoustic transducer of the implant detects an externalacoustic signal, e.g., having a particular frequency, such as thetransducer's resonant frequency, the voltage on the transistor Q1 willexceed the transistor threshold voltage of about one half of a volt.Transistor Q1 is thereby switched on and current flows throughtransistor Q1 and pull-up resistor R2. As a result of the current flowthrough transistor Q1, the voltage on the drain of transistor Q1 and thegate of transistor Q2 drops from +3V substantially to zero (ground).This drop in voltage switches on the P-channel transistor Q2, whichbegins to conduct current through transistor Q2 and pull-down resistorR3.

[0048] As a result of the current flowing through transistor Q2, thevoltage on the drain of transistor Q2 and the gates of transistors Q3and Q4 increases from substantially zero to +3V. The increase in voltageswitches on transistors Q3 and Q4. As a result, transistor Q3 begins toconduct current through resistor R4 and main switching transistor Q4begins to conduct current through the “load,” thereby switching on theelectrical circuit.

[0049] As a result of the current flowing through transistor Q3, thegate of transistor Q2 is connected to ground through transistor Q3,irrespective of whether or not transistor Q1 is conducting. At thisstage, the transistors (Q2, Q3 & Q4) are latched to the conductingstate, even if the piezoelectric voltage on transistor Q1 issubsequently reduced to zero and transistor Q1 ceases to conduct. Thus,main switching transistor Q4 will remain on until switch S1 is opened.

[0050] In order to deactivate or open the switch 400, switch S1 must beopened, for example, while there is no acoustic excitation of thepiezoelectric transducer. If this occurs, the gate of transistor Q2increases to +3V due to pull-up resistor R2. Transistor Q2 then switchesoff, thereby, in turn, switching off transistors Q3 and Q4. At thisstage, the switch 400 returns to its sleep mode, even if switch S1 isagain closed. The switch 400 will only return to its active mode uponreceiving a new acoustic activation signal from the piezoelectrictransducer.

[0051] It should be apparent to one of ordinary skill in the art thatthe above-mentioned electrical circuit is not the only possibleimplementation of a switch for use with the present invention. Forexample, the switching operation my be performed using a CMOS circuit,which may draw less current when switched on, an electromechanicalswitch; and the like.

[0052] Turning to FIGS. 3 and 4, a system 410 is shown for communicatingwith an implant 412, such as one of those described above. Generally,the system 410 includes an external communications device or controller414, and may include a charger 416, one or more implants 412 (only oneshown for simplicity), and an external recorder, computer, or otherelectronic device 434.

[0053] With particular reference to FIG. 4, the external controller 414may include a processor or other electrical circuit 418 for controllingits operation, and an energy source 420, e.g., a nonrechargeable or arechargeable battery, coupled to the processor 418 and/or othercomponents of the controller 414, such as a power amplifier or anoscillator (not shown). In addition, the controller 414 may include oneor more acoustic transducers 422 that are configured for convertingbetween electrical energy and acoustic energy, similar to thosedescribed above. As shown, a single acoustic transducer 422 is providedthat may communicate using acoustic telemetry, i.e., capable both ofconverting electrical energy to acoustic energy to transmit acousticsignals, and converting acoustic energy to electrical energy to receiveacoustic signals, as explained further below. Alternatively, separateand/or multiple acoustic transducers may be provided for transmittingand receiving acoustic signals.

[0054] In one embodiment, the controller 414 also includes memory 424coupled to the processor 418, e.g., for storing data provided to thecontroller 414, as explained further below. The memory 424 may be atemporary buffer that holds data before transfer to another device, ornon-volatile memory capable of storing the data substantiallyindefinitely, e.g., until extracted by the processor 418 or otherelectronic device. For example, the memory 424 may be a memory card oran eprom (not shown) built into the controller 414 or otherwise coupledto the processor 418. The controller 414 may also include an interface426, such as a lead or connector, or a transmitter and/or receiver, thatmay communicate with the external electronic device, as explainedfurther below.

[0055] Preferably, the controller 414 is carried by a patch 415 that maybe secured to a patient, e.g., to the patient's skin 92. For example,the patch 415 may include one or more layers of substantially flexiblematerial to which the controller 414 and/or its individual componentsare attached. The patch 415 may include a single flexible membrane (notshown) to which the controller 414 is bonded or otherwise attached,e.g., using a substantially permanent adhesive, which may facilitate thepatch 415 conforming to a patient's anatomy. Alternatively, thecontroller 414 may be secured between layers of material, e.g., within apouch or other compartment (not shown) within the patch 415. Forexample, the patch 415 may include a pair of membranes (not shown)defining the pouch or compartment. The space within which the controller414 is disposed may be filled with material to acoustically couple theacoustic transducer(s) (formed, for example, from PZT, composite PZT,Quartz, PVDF, and/or other piezoelectric material) of the controller 414to an outer surface of the patch 415. Alternatively, the acoustictransducer(s) may be exposed, e.g., in a window formed in a wall of thepatch 415.

[0056] The patch 415 may be formed from a flexible piezoelectricmaterial, such as PVDF or a PVDF copolymer. Such polymers may allow thepatch 415 to produce ultrasonic waves, as well as allowing thecontroller 414 to be secured to the patient's skin 92. Thus, the wall ofthe patch 415 itself may provide an acoustic transducer for thecontroller 414, i.e., for transmitting acoustic energy to and/orreceiving acoustic energy from the implant 412.

[0057] The patch 415 may then be secured to the patient's skin 92 usinga material, such as a layer of adhesive (not shown), substantiallypermanently affixed or otherwise provided on a surface of the patch. Theadhesive may be hydrogel, silicon, polyurethane, polyethylene,polypropylene, fluorocarbon polymer, and the like. Alternatively, aseparate adhesive may be applied to the patch 415 and/or to thepatient's skin 92 before applying the patch 415 in order to secure thecontroller 414 to the patient's skin 92. Such an adhesive may enhanceacoustically coupling of the acoustic transducer(s) of the controller414 to the patient's skin 92, and consequently to the implant 412 withinthe patient's body 94. Optionally, additional wetting material,including water, silicone oil, silicone gel, hydrogel, and the like,and/or other acoustically conductive material may be provided betweenthe patch 415 or the acoustic transducer 422, and the patient's skin 92,e.g., to provide substantial continuity and minimize reflection or otherlosses and/or to secure the patch 415 to the patient.

[0058] Alternatively, the controller 414 may be carried by a belt (notshown) that may be secured around the patient, e.g., such that theacoustic transducer 422 is secured against the patient's skin. The beltmay carry other components of the system 410, e.g., an external powersupply for the controller 414. For example, a battery pack (not shown)may be carried by the belt that may be coupled to the controller 414 forproviding electrical energy for its operation.

[0059] The patch 415 may be relatively light and compact, for example,having a maximum surface dimension (e.g., width or height) not more thanabout ten to two hundred millimeters (10-200 mm), a thickness not morethan about five to one hundred millimeters (5100 mm), and a weight notmore than about twenty to four hundred grams (20-400 g), such that thecontroller 414 may be inconspicuously attached to the patient. Thus, thepatient may be able to resume normal physical activity, withoutsubstantial impairment from the controller. Yet, the internal energysource of the controller 414 may be sufficiently large to communicatewith the implant 412 for an extended period of time, e.g., for hours ordays, without requiring recharging or continuous coupling to a separateenergy source.

[0060] The system 410 may be used to control, energize, and/or otherwisecommunicate with the implant 412. For example, the controller 414 may beused to activate the implant 412. One or more external acoustic energywaves or signals 430 may be transmitted from the controller 414 into thepatient's body 94, e.g., generally towards the location of the implant412 until the signal is received by the acoustic transducer (not shownin FIGS. 3 and 4) of the implant 412. Upon excitation by the acousticwave(s) 430, the acoustic transducer produces an electrical output thatis used to close, open, or otherwise activate the switch (also not shownin FIGS. 3 and 4) of the implant 412. Preferably, in order to achievereliable switching, the acoustic transducer of the implant 412 isconfigured to generate a voltage of at least several tenths of a voltupon excitation that may be used as an activation signal to close theswitch, as described above.

[0061] As a safety measure against false positives (e.g., erroneousactivation or deactivation), the controller 414 may be configured todirect its acoustic transducer 422 to transmit an initiation signalfollowed by a confirmation signal. When the acoustic transducer of theimplant 412 receives these signals, the electrical circuit may monitorthe signals for a proper sequence of signals, thereby ensuring that theacoustic switch of the implant 412 only closes upon receiving the properinitiation and confirmation signals. For example, the acoustic switchmay only acknowledge an activation signal that includes a first pulsefollowed by a second pulse separated by a predetermined delay. Use of aconfirmation signal may be particularly important for certainapplications, for example, to prevent unintentional release of drugs bya drug delivery implant.

[0062] In addition to an activation signal, the controller 414 maytransmit a second acoustic signal that may be the same as or differentthan the acoustic wave(s) used to activate the acoustic switch of theimplant 412. Thus, the switch may be opened when the acoustic transducerof the implant 412 receives this second acoustic signal, e.g., by theacoustic transducer generating a termination signal in response to thesecond acoustic signal, in order to return the implant 412 to its sleepmode.

[0063] For example, once activated, the switch may remain closedindefinitely, e.g., until the energy storage device (not shown in FIGS.3 and 4) of the implant 412 is completely depleted, falls below apredetermined threshold, or until a termination signal is received bythe acoustic transducer of the implant 412 from the controller 414.Alternatively, the acoustic switch of the implant 412 may include atimer (not shown), such that the switch remains closed only for apredetermined time, whereupon the switch may automatically open,returning the implant 412 to its sleep mode.

[0064]FIG. 5 shows an alternative embodiment of an implant 510 that doesnot include an acoustic switch. Generally, the implant includes a sensor512, one or more energy transducers 514, one or more energy storagedevices 516, and a control circuit 518, similar to the embodimentsdescribed above. The sensor 512 is preferably a pressure sensor formeasuring intra-body pressure, such as an absolute variable capacitancetype pressure sensor. In alternative embodiments, one or more othersensors may be provided instead of or in addition to a pressure sensor512. For example, the sensor 512 may include one or more biosensorscapable of measuring physiological parameters, such as temperature,electrical impedance, position, strain, pH, fluid flow, and the like. Anexternal controller (not shown), such as that described above, may alsobe used to communicate with this implant.

[0065] Returning to FIG. 3, an external controller 414 in accordancewith the present invention preferably has only sufficient power tocontrol its own operation and to communicate with the implant 412.Because of its limited energy requirements, the controller 414 may berelatively small and portable, e.g., may be attached to the patient,while still allowing the patient to engage in normal physical activity.The controller 414 may be used to communicate with the implant 412,e.g., periodically activating or deactivating the implant 412, and/orrecording data generated and transmitted by the implant 412. Because itis located outside the patient's body, the controller 414 may be moreeasily programmed or reprogrammed than the implant 412 itself, and/ormay be repaired or replaced if necessary or desired.

[0066] In addition to the external controller 414, the system 410 mayinclude one or more electronic devices 434 that may be coupled to thecontroller 414 via the interface 426, such as a recorder, a computer, apersonal digital assistant, and/or a wireless device, such as a cellulartelephone. The electronic device 434 may be directly coupled to thecontroller 414, by a connector or lead (not shown) extending from thepatch 415 within which the controller 414 is provided. Alternatively,the controller 414 and/or patch 415 may include a wireless transmitterand/or receiver (not shown), e.g., a short-range RF transceiver, forcommunicating with the electronic device 434.

[0067] The electronic device 434 may be used to extract data from thememory 424 of the controller 414, e.g., sensor data and the like,received from the implant 412. This data may be included in a patientdatabase maintained by health care professionals monitoring the patientreceiving the implant 412. In addition, the electronic device 434 may beused to program the controller 414, e.g., to program commands, timingsequences, and the like.

[0068] The system 410 may also include an external charger 418. Forexample, the implant 412 may include a rechargeable energy storagedevice (not shown in FIG. 3), preferably one or more capacitors, thatare coupled to the acoustic transducer (also not shown in FIG. 3). Thecharger 416 may include a probe 428, including an acoustic transducer430 for contacting a patient's skin 92. The charger 416 also includes asource of electrical energy 432, such as a radio frequency (RF)generator, that is coupled to the acoustic transducer 430. The charger418 may also include electrical circuits for controlling its operationand buttons or other controls (not shown) for activating and/ordeactivating the acoustic transducer 430.

[0069] The charger 418 may be used to charge or recharge the implant,e.g., periodically or before each activation. Because the charger 418includes a substantially more powerful energy source than the controller414, the charger 418 is generally a relatively bulky device compared tothe controller 414, in particular due to the energy generator, which maybe stationary or of limited mobility. In addition, the charger 418 maybe used to recharge the controller 414 periodically, e.g., by a director wireless coupling. Alternatively, the controller 414 and patch 415may be disposable, e.g., after its energy has been depleted, andreplaced with another.

[0070] For purposes of comparison, an exemplary charger 416 may need togenerate about ten kiloPascals (10 kPa) of acoustic energy for abouttwenty seconds (20 sec.) in order to fully charge the implant 412. Incontrast, an exemplary controller 414 may be limited to outputtingrelatively smaller bursts of acoustic energy for communicating with, butnot charging, the implant 412. Such acoustic signals may have a durationof as little as about one millisecond (1 ms), as opposed to thesignificantly longer charging signals generated by the charger 416.

[0071] The transducer 422 of the controller 414 may consume about oneWatt (1 W) of power to produce a 1 kPa acoustic signal for about onemillisecond. If the controller 414 communicates with the implant 412 onan hourly basis, the energy source 420 of the controller 418 may onlyneed sufficient capacity to provide 0.024 Watt seconds per day (0.024W.sec./day). Because of this low energy requirement, the energy source420, and, consequently, the controller 418, may be relatively compactand portable, as compared to the charger 416. Thus, the energy source420 may be self-contained within the controller 418, i.e., carried bythe patch 415. Alternatively, a portable energy source, e.g., anexternal battery pack (not shown) may be provided for supplyingelectrical energy to the controller 418 that may be carried by thepatient, e.g., on a belt (not shown).

[0072] In an alternative embodiment, the controller and charger may beprovided as a single device (not shown), e.g., including one or moreacoustic transducers and/or one or more processors for performing thefunctions of both devices, as described above. In this embodiment, theimplant 412 may operate in a “half-duplex” mode, a quasi-continuousmode, or in a “full-duplex” mode, as described in the applicationsincorporated above.

[0073]FIGS. 6 and 7 show another embodiment of an implant 10, inaccordance with the present invention. Generally, the implant 10includes a sensor 12, one or more energy transducers 14, one or moreenergy storage devices 16, and a controller 18.

[0074] The sensor 12 is preferably a pressure sensor for measuringintra-body pressure. The sensor 12 may measure pressure within a rangeas low as a few millibars gauge (e.g., pressure ranges experiencedwithin the cranium or within the pulmonary artery) and up to about 400millibars gauge (e.g., blood pressure ranges experienced duringsystole). In addition, because the barometric pressure may vary bylocation, i.e., altitude, the absolute pressure range capacity of thesensor is preferably between about 650 and 1450 millibars absolute.

[0075] The sensor 12 can be an absolute variable capacitance typepressure sensor. Alternatively, a piezoresistive pressure sensor may beused, although the energy consumption of this type of sensor may besubstantially higher than a variable capacitance pressure sensor. Forexample, a typical piezoresistive sensor may have a bridge resistance ofabout five kiloohms (5 kΩ). Assuming that one volt (1 V) is sufficientto allow pressure sampling, a current of at least about 0.2 milliAmperes(mA) would be required to operate the sensor. This may be about onehundred times more than the current required to obtain pressure samplesusing a variable capacitance pressure sensor.

[0076] Some reduction in power consumption of piezoresistive pressuresensors may be obtained by reducing the sampling rate of the sensor orotherwise reducing the duty cycle of the implant. Alternatively, toreduce power consumption, a sample-and-hold circuit (not shown) may beprovided for capturing voltages, and an analog-to-digital converter(also not shown) may be provided for converting the voltages whendesired. Thus, the current may be on for relatively short times duringeach sampling cycle.

[0077] Preferably, a silicon MEMS-based pressure sensor is used, becauseof its relative small size, e.g., smaller than about four millimeters (4mm) maximum footprint, e.g., not more than about four millimeters (4 mm)width by four millimeters (4 mm) length. Preferably, the sensor is nolarger than about 0.8 mm width by about 2.1 mm length by about 0.3 mmthickness. Silicon is a particularly useful material for the sensor 12,as it generally does not suffer from creep and fatigue, and thereforemay result in a substantially stable sensor. MEMS-based sensors arepresently preferred because they may be manufactured in large volume atrelatively low cost compared to other sensors. Other materials that maybe used include titanium, as is used for the Chronicle™ devicemanufactured by Medtronic, Inc. Preferably, the sensor 12 is made frombiocompatible materials, although the sensor 12 may be coated, ifnecessary or desired, with a biocompatible and/or chemically resistivecoating (not shown), as will be appreciated by those skilled in the art.

[0078] In alternative embodiments, one or more other sensors may beprovided instead of or in addition to a pressure sensor. For example,the sensor 12 may include one or more biosensors capable of measuringphysiological parameters, such as temperature, electrical impedance,position, strain, pH, fluid flow, and the like. U.S. Pat. Nos. 4,793,825issued to Benjamin et al. and 5,833,603 issued to Kovacs et al. discloseadditional exemplary embodiments of biosensors that may be provided. Thedisclosure of these references and others cited therein are expresslyincorporated herein by reference. The sensor 12 may generate a signalproportional to a physiological parameter that may be processed and/orrelayed by the controller 18 to the energy transducer 14, as describedfurther below. Alternatively, the sensor 12 may be configured to monitora radiation dose including ionizing, magnetic and/or acoustic radiation,to monitor flow in a bypass graft, to produce cell oxygenation andmembrane electroporation, and the like.

[0079] In further alternatives, a device for providing one or moretherapeutic functions (not shown) may be provided in addition to orinstead of the sensor 12. For example, the device may be used toactivate and/or control a therapeutic device implanted within apatient's body, such as an atrial defibrillator, a pain reliefstimulator, a neuro-stimulator, a drug delivery device, and/or a lightsource used for photodynamic therapy.

[0080] Turning to FIGS. 8A and 8B, the energy transducer 14 ispreferably an acoustic transducer for converting energy betweenelectrical energy and acoustic energy. As explained further below, theacoustic transducer 14 is configured for converting acoustic energy froma source external to the implant into electrical energy and/or fortransmitting an acoustic signal including sensor data to a locationexternal to the implant. In one embodiment, the energy transducer 14 isconfigured to operate alternatively as either an energy exchanger or anacoustic transmitter, or simultaneously as an energy exchanger and anacoustic transmitter. Alternatively, multiple energy transducers (notshown) may be provided, e.g., one or more converting acoustic energystriking the energy exchanger into electrical energy, and one or moretransmitting acoustic signals to a location external to the implant 10.In a further alternative, multiple energy transducers (not shown) may beprovided for increasing the electrical energy produced for a givenacoustic energy transmitted to the implant 10.

[0081] The energy transducer 14 generally includes a substrate 20including one or more cavities 22 therein, such as the array of cavities22 shown in FIG. 8A. The cavities 22 may extend completely through thesubstrate 20 or only partially into the substrate 20. The cavities 22are preferably substantially round in cross-section, although oval orother elongate slotted cavities (not shown) may be provided, which mayincrease sensitivity and/or efficiency as compared to a substantiallyround cavity. The cavities 22 may have a cross-section of about 0.52.5millimeters, and preferably between about 1.0 and 1.3 millimeters (mm).For elliptical or other elongate cavities (not shown), the cavitiespreferably have a width of 0.2-2.5 millimeters and a length of 1.0-25millimeters. The substrate 20 may be formed from a relatively highmodulus polymer, such as poly ether ether ketone (PEEK), silicon, and/ora printed circuit board, e.g., of FR4, Rogers, a ceramic, or Kapton.

[0082] A substantially flexible piezoelectric layer 24 is attached tothe substrate 20 across cavities 22. The piezoelectric layer 24generally includes a polymer layer 28, preferably a fluorocarbonpolymer, such as poly vinylidene fluoride (PVDF). The polymer layer 28may have a thickness of between about three and two hundred fiftymicrometers (3-250 μm), and preferably about thirty micrometers (30 μm)or less. A first conductive layer 30 is provided on an external surfaceof the polymer membrane 28 and a second conductive layer 32 provided onan internal surface of the polymer membrane 28. The second conductivelayer 32 may be coupled to a conductive region 36 provided on a wall ofthe cavities 22. A pad 34 is provided on a lower surface of thesubstrate 20 for coupling the second conductive layer 32 to a printedcircuit board (not shown), as described further below.

[0083] To manufacture the energy transducer 14, a substantially flexiblepolymer layer 28, such as a PVDF membrane, is provided. Because PVDF isgenerally chemically inert, the polymer layer 28 may need to beactivated, e.g., using an etching process. For example, a sodiumnapthalene solution may be used to chemically attack the PVDF to cleavethe carbonfluorine bonds and/or other solutions to cleave thecarbon-hydrogen bonds and/or carbon-carbon bonds in the material.Alternatively, a gas phase plasma treatment, e.g., using an oxygen, air,Helium, and/or Argon plasma, may be used.

[0084] A substantially planar substrate 20 is provided, and one or morecavities 22 are formed in a surface of the substrate 20, for example, bymechanical drilling, laser drilling, or punching. Alternatively, thecavities 22 may be etched into the substrate 20, e.g., usingVLSI/micro-machining technology or any other suitable technology.

[0085] A thin layer of adhesive (not shown) may be applied over thesubstrate 20, such as an epoxy or acrylic-based adhesive. Preferably, arelatively low viscosity (e.g., less than one thousand centi-poise)adhesive is used that may be atomized over the substrate 20. Morepreferably, the adhesive is light-activated, thereby facilitatingpositioning of the piezoelectric layer 24 over the substrate 20 beforethe adhesive is cured. The piezoelectric layer 24 is applied against theadhesive over the substrate 20. Alternatively, individual piezoelectriclayers (not shown) may be bonded or otherwise attached over one or moreindividual cavities 22. The cavities 22 may be filled with a gas, suchas air, to a predetermined pressure, e.g., ambient pressure or apredetermined vacuum, that may be selected to provide a desiredsensitivity and ruggedness for the energy transducer 14.

[0086] The assembled substrate 20 and piezoelectric layer 24 may beplaced in a pressure chamber, and a predetermined pressure appliedagainst the piezoelectric layer 24. This may cause the piezoelectriclayer 24 to press against the substrate 20, e.g., to facilitatespreading the adhesive more evenly between the substrate 20 and thepiezoelectric layer 24. In addition, the predetermined pressurepreferably causes the piezoelectric layer 24 to at least partially enterthe cavities 22, thereby creating depressions in the piezoelectric layer24 corresponding to the cavities 22, as best seen in FIG. 8B.Optionally, the pressure chamber may be heated to a predeterminedtemperature to facilitate creating the depressions and/or cure theadhesive. In addition or alternatively, the adhesive may then be cured,e.g., by exposing the assembled substrate 20 and piezoelectric layer 24to visible or ultraviolet light, pressure, and/or heat for apredetermined time.

[0087] Thus, the piezoelectric layer 24 may include depressions, whichmay be useful for enhancing the efficiency and/or sensitivity of theenergy transducer 12. For example, the depressions may enhance theconversion of an acoustic pressure wave striking the piezoelectric layer24 into mechanical strain, resulting in an increased yield of electricalenergy for a given pressure amplitude. The depressions may also be usedto customize the natural resonant frequency of the piezoelectric layer24. The depth of the depressions may be between about one and twohundred micrometers (1-200 μm), and preferably between about twenty andone hundred micrometers (20-100 μm), although depths greater than thismay also increase efficiency as compared to a planar piezoelectric layer24 without depressions. To ensure that these depths are consistentlyreproducible, the depth of the depressions may be measured, for example,using a non-contact optical profiler.

[0088] Both surfaces of the polymer layer 28 may be coated withconductive layers 30, 32, preferably metallization layers, at any stageof manufacturing. For example, the conductive layers 30, 32 may beapplied either before or after the piezoelectric layer 24 has beenbonded to the substrate 20. Because the current encountered during useof the energy transducer 14 is relatively low (e.g., about thirtymicroamperes (30 μA) or less, and preferably about five microamperes (5μA) or less), a thickness of the conductive layers 30, 32 may berelatively thin, e.g., fifteen micrometers (15 μm) or less, and morepreferably about two hundred nanometers (200 nm) or less. The thicknessof the conductive layers 30, 32 may be substantially equal to ordifferent from one another. For example, the first or outer conductivelayer 30 may be substantially thicker than the second or innerconductive layer 32 to protect the energy transducer 14 fromenvironments to which it is exposed, such as those encountered within ahuman body. The conductive layers 30, 32 may be formed frombiocompatible and/or metallic materials, including one or more of gold,platinum, titanium, tantalum, palladium, vanadium, copper, nickel,silver, and the like.

[0089] The conductive layers 30, 32 may be coated on the surfaces of thepolymer layer 28 using any known method, such as depositing anelectro-less nickel, gold, or copper base layer, followed by depositinga galvanic coating, including any of the materials listed above. Theconductive layers 30, 32 may be deposited using physical vapordeposition, chemical vapor deposition, sputtering, and/or other gasphase coating processes known to those skilled in the art. Theconductive layers 30, 32 may be applied as single layers or as multiplelayers of one or more materials in order to optimize the layers'electrical, mechanical, and/or chemical properties. Exemplary methodsfor making the piezoelectric layer 24 may be found in “Handbook ofPhysical Vapor Deposition (PVD) Processing,” Donald M. Mattox (ISBN0-8155-1422-0 Noyes publications, 1998) and “Handbook of DepositionTechnologies for Films and Coatings,” Rointan F. Bunshah (ed.), (NoyesPublications; ISBN: 0815513372 2nd edition 1994.) The disclosures ofthese references, as well as any others cited therein, are incorporatedherein by reference.

[0090] The method described above may be used to make individual energytransducers or alternatively to make a plurality of energy transducers.For example, a plurality of energy transducers may be made as a singlepanel, and, after the metallization process, the panel may be separatedinto individual energy transducers. The separation may be accomplishedusing known dicing systems and methods, for example, using a dicingmachine known to those in the microelectronics industry for dicingsilicon wafers, a knife cutter, a milling machine, or a laser, e.g., adiode laser, a neodymium YAG laser, a CO₂ laser, or an excimer laser.Upon separation of the individual energy transducers, the electricalimpedance of each of the energy transducers may be measured to confirmtheir integrity and proper operation. Additional information on acoustictransducers or energy exchangers appropriate for use with implants inaccordance with the present invention may be found in U.S. Pat. No.6,140,740, the disclosure of which is expressly incorporated herein byreference.

[0091] In an alternative embodiment, the substrate 20 may be formed fromsilicon, with or without electronics. The cavities 22 may be formedtherein, the piezoelectric layer 24 may be attached to the substrate 20,and the surfaces metalized, generally as described above. In order toavoid large capacitances, an insulating oxide or other ring (not shown)may be provided around the cavities 22. The bottom of the cavities 22may be sealed using an adhesive, e.g., an underfill adhesive used duringthe flip-chip process.

[0092] Returning to FIGS. 6 and 7, the energy storage device 16,preferably one or more capacitors, is coupled to the energy transducer14. In an exemplary embodiment, the capacitor may be a tantalum orceramic capacitor, e.g., a 10.0° F. tantalum capacitor, such as modelno. TACL106K006R, sold by AVX. Alternatively, the energy storage device16 may be a battery or other known device, preferably capable of storingelectrical energy substantially indefinitely. In addition, the energystorage device 16 may be capable of being charged from an externalsource, e.g., using acoustic energy, as described further below. In analternative embodiment, the energy storage device 16 may include both acapacitor and a primary, non-rechargeable battery (not shown).Alternatively, the energy storage device 16 may include a secondary,rechargeable battery and/or capacitor that may be energized beforeactivation or use of the implant 10. For example, the energy storagedevice 16 may include a first relatively fast-charging capacitor and asecond relatively slow-charging capacitor (not shown).

[0093] Turning to FIG. 7, the controller 18 may be an ApplicationSpecific Integrated Circuit (ASIC) and/or a plurality of discreteelectronic components. The controller 18 generally interfaces betweenthe sensor 12, the energy transducer 14, and/or other active or passivecomponents of the implant 10. The controller 18 is also coupled to theenergy storage device 16 for receiving electrical energy to operate thecontroller 18 and/or other components of the implant 10. The controller18 generally includes a rectifier 40, reset and threshold circuitry 42,signal detect circuitry 44, transmission circuitry 46, a clockoscillator 48, an analog-to-digital converter 50, and power managementand control logic circuitry 52. In addition, the controller 18 mayinclude a voltage reference circuit, e.g., a bandgap reference, a Zenerdevice, or a buried Zener device.

[0094] The rectifier 40 is coupled to the energy transducer 14 forconverting electrical. energy generated by the energy transducer 14 intoa form suitable for powering components of the implant 10. For example,the rectifier 40 may be configured for converting incoming alternatingcurrent (AC) voltage from the energy transducer 14 into direct current(DC) voltage for storage by the energy storage device 16 and/or forpowering the controller 18 and other components of the implant 10. Therectification may be performed by diodes arranged in a configurationsuitable for the requirements of the mode of operation, preferablyresulting in a passive circuit that draws substantially no current.

[0095]FIG. 9 shows a first embodiment of a full-bridge rectifier 40′that may be provided. The energy transducer 14 and energy storage device16 may be connected to the rectifier 40′ such that AC current generatedby the energy transducer 14 is converted into DC current for chargingthe energy storage device 16. The full-bridge configuration of therectifier 40′ may yield relatively high current and power efficiencythat may be suitable for “full-duplex” operation of the energytransducer 14, i.e., where the energy transducer 14 simultaneouslyconverts external acoustic energy into electrical energy and transmitsan acoustic signal.

[0096]FIG. 10 shows a second embodiment of a voltage-doubler rectifier40″ that may be used. The configuration of this rectifier 40″ may yieldless current than the rectifier 40′ shown in FIG. 9, although it maygenerate a relatively higher voltage for a given acoustic excitation ofthe energy transducer 14. This rectifier 40″ may be better suited for“half-duplex” operation, i.e., where the energizing and transmittingfunctions of the energy transducer 14 are temporally distinct. Thisembodiment may also only require two diodes to operate and may keep oneside of the energy transducer 14 substantially grounded, therebysimplifying construction of the implant 10.

[0097] Alternatively, other rectification circuits (not shown) may beused, including Schottky diodes, voltage triplers or other multipliercircuits, and the like. In addition, the rectifier 40 may include anovervoltage protector (not shown), which may prevent the energy storagedevice 16 from overcharging, e.g., to unsafe levels. For example, theovervoltage protector may include a Zener diode, or a transistor thatopens at a predetermined threshold voltage.

[0098] Returning to FIG. 7, the reset and threshold circuitry 42 iscoupled to the energy storage device 16 for monitoring for particularevents. For example, the reset and threshold circuitry 42 may reset thecontroller 18 as the energy storage device 16 is recharging. This“power-on” reset function may occur when the capacitor voltage of theenergy storage device 16 reaches a predetermined charging voltage, e.g.3.8 V. In addition, during operation of the implant 10, the reset andthreshold circuitry 42 may automatically turn the controller 18 and/orother components of the implant 10 off when the capacitor voltage of theenergy storage device 16 drops below a predetermined shut-down voltage,e.g., 1.5 V.

[0099] The reset circuitry 42 preferably monitors the voltage of theenergy storage device 18 in a substantially passive manner. For example,the reset circuitry 42 may include a fieldeffect transistor (FET) thatis switched on when its gate voltage exceeds a predetermined threshold.Thus, the reset circuitry 42 may be passive, i.e., drawing substantiallyno current from the energy storage device 16.

[0100] The signal detect circuitry 44 generally is coupled to the energytransducer 16 for monitoring when the energy transducer 16 is receivingacoustic signals from a source external to the implant 10. Preferably,the signal detect circuitry 44 is a passive FET circuit, thereby drawingsubstantially no current. The signal detect circuitry 44 may alsoinclude a smoothing capacitor (not shown) and/or logic for reducing thesensitivity of the signal detect circuitry 44 to spurious transientsignals. The signal detect circuitry 44 may provide a communicationchannel into the implant 10, e.g., to pass commands and/or informationin the acoustic excitation signals received by the energy transducer 16for use by the controller 18. In addition, the signal detect circuitry44 may pass commands or other signals to controller 18, e.g., thatacoustic excitation signals have been discontinued, and/or that theimplant 10 should become operative. For example, when the implant 10 isconfigured for operation in half-duplex mode, the signal detectcircuitry 44 may monitor for termination of an energizing transmissionfor charging the energy storage device 16, whereupon the controller 18may begin sampling and/or transmitting sensor data.

[0101] The transmission circuitry 46 is coupled to the energy transducer14, and is generally responsible for preparing signals for transmissionfrom the implant 10 to a location exterior to the implant 10. Thesignals are preferably digital electrical signals, which may begenerated, for example, by grounding one pin of the energy transducer 14and alternately connecting the other pin between ground and apredetermined voltage. Alternatively, the signals may be generated byalternately grounding the first pin and connecting the second pin to thepredetermined voltage, and then grounding the second pin and connectingthe first pin to the predetermined voltage. In a further alternative,the signal may be processed or modulated, e.g., using spread spectrum,direct sequence mixing, CDMA, or other technologies, as will beappreciated by those skilled in the art.

[0102]FIG. 11 shows an exemplary embodiment of a transmission circuit46′ that may be used for transmitting such digital signals. The energytransducer 14 is coupled to ground and between a pair of transistors 47₁′ and 47 ₂′. The gates of the transistors 47 ₁′ and 47 ₂′ may becoupled to the control logic circuitry 52 (shown in FIG. 7) forreceiving signals for transmission, such as sensor data signals from thesensor 12 (also shown in FIG. 7). Alternatively, the gates may becoupled directly to the analog-to-digital converter 50 (also shown inFIG. 7) or to the sensor 12. The incoming sensor data signals mayalternatively couple the energy transducer 14 between ground and +V,thereby converting the sensor data signals into acoustic energy, whichmay be transmitted to a location exterior to the implant 10.

[0103]FIG. 12 shows another embodiment of a transmission circuit 46″that may be provided for full-duplex operation, i.e., for simultaneouslyreceiving an energizing signal and transmitting a data signal. Forexample, the energy transducer 14 may receive an energizing signal at afirst frequency f₁, while the transmission circuit switches thetransistor 49 on and off at a second frequency f₂, e.g., using sensordata signals. This periodic switching induces a current in the energytransducer 14 at frequencies f₁+/−f₂ and possibly others. This currentcauses the energy transducer 14 to transmit acoustic signals at the newfrequencies, which may be correlated back to the sensor data by areceiver exterior to the implant 10. In a further alternative, thetransmission circuitry 46 may include analog circuitry for generatinganalog signals that may be transmitted by the energy transducer 14.

[0104] In an alternative embodiment (not shown), a full-bridgetransmission circuit may be used for the transmission circuit. Usingthis circuit, pins of the energy transducer may be coupled alternatelyto ground and +V. For example, a first pin may be coupled to ground anda second pin coupled to +V, and then the first pin may be coupled to +Vand the second pin coupled to ground. This circuit may generate signalsat about twice the amplitude of the other embodiments described above.

[0105] Returning to FIG. 7, the clock oscillator 48 may provide timingand/or clocking signals for the controller 18 and/or the variouscomponents of the implant 10. For example, the clock oscillator 48 maygenerate signals at fixed frequencies between about twenty and sixtykilohertz (20-60 kHz).

[0106] The analog-to-digital (A/D) converter 50 is coupled to the sensor12, and to the control logic circuitry 52 or directly to thetransmission circuit 46. The A/D converter 50 may digitize the sensoroutput for further processing by the controller 18 and/or fortransmission by the energy transducer 14, using one of a variety ofknown digitization systems. For a variable capacitance pressure sensor,a switched-capacitor sigma-delta converter may be provided.Alternatively, for piezo-resistive or strain-gauge sensors, a track andhold amplifier followed by a successive approximation converter may beprovided.

[0107] The A/D converter 50 may also include a calibrated voltagereference, against which measurements may be performed. Preferably, thisis a bandgap reference, based upon the properties of silicontransistors. Alternatively, other reference circuits, such as Zener orburied Zener diode references, may be used.

[0108] The power management and control logic circuitry 52 may includeseveral subsystems, such as a power management unit, a receptiondecoder, a transmission encoder, a state machine, and/or a diagnosticunit (not shown), which may be discrete hardware components and/orsoftware modules. For example, an ASIC-compatible microprocessor, suchas a CoolRISC processor available from Xemics, may be used for the powermanagement and control logic circuitry 52. The power management unit maybe provided for switching current on and off and/or for biasing voltagesof the various components of the controller 18, particularly for anyanalog subcircuits, on demand. Thus, power may be supplied only to thoseportions or components currently in need of power, in order to conserveresources of the implant 10. The reception decoder is coupled to thesignal detect circuitry 44 for decoding signals extracted by the signaldetect circuitry 44 into commands to be passed to other components ofthe implant 10. These commands may include initialization,identification, control of system parameters, requests for sensor dataor other information, and the like.

[0109] The transmission encoder is coupled to the transmission circuitry46 and generally latches digital information supplied by the A/Dconverter 50 and prepares it for serial transmission by the transmissioncircuitry 46. The information may include an acknowledgement symbol, anidentification code (e.g., a model, a serial number, or other identifieridentifying the implant 10), internal status information (such ascapacitor voltage), and/or measurements obtained by the sensor 12. Datamay be sent using an asynchronous serial protocol, including, forexample, a start bit, one or more synchronization bits, eight bits ofdata, a parity bit, and/or a stop bit. The data transmission rate andbit structure are preferably constructed so as to avoid data corruptiondue to reflections and reverberations of the acoustic signal within abody. For example, each bit of information may be made up of sixteenoscillations of the acoustic wave in order to ensure fidelity of thetransmission. In addition, there may be predetermined delays betweensequential transmissions, e.g., to minimize interference and/or to allowreverberations to die out.

[0110] The state machine controls the operational mode of the controllogic circuitry 52. For example, it may determined the current mode(e.g., idle, decode, sample, transmit, and the like), and may containlogic for switching from one mode to another.

[0111] The diagnostic unit may include circuits used duringmanufacturing and/or calibration of the implant 10. This unit may not beoperational after system integration, but may be awakened periodicallyby external command, e.g., to conduct in-vivo system diagnostics.

[0112] Turning to FIG. 6, to manufacture an implant 10, in accordancewith the present invention, the various components may be assembled ontoa double-sided printed circuit board (PCB) 11. The PCB 11 is preferablymade from FR4 or other materials commonly used in the semiconductorindustry, such as polyamide, Rogers, a ceramic, or Teflon™. The PCB 11may have a thickness of between about ten and one thousand micrometers(10-1000 μm), and preferably about 0.25 millimeter (mm) or less. Thesensor 12 and controller 18 may be flip chip bonded or wire bonded toone side of the PCB 11, e.g. using anistropic glue, a conductiveadhesive, a nonconductive adhesive, or solder bumps. The active sensingarea of the sensor 12 may be exposed through an opening 13 in the PCB11, since the sensing area may be disposed on the same side as theelectrical pads (not shown).

[0113] Alternatively, a single-sided PCB may be used, which may resultin an implant that has a smaller thickness, but which may be longer orwider to accommodate the circuits printed thereon. A longer, thinnerimplant may be useful for implantation in particular locations within apatient's body, as will be appreciated by those skilled in the art. In afurther alternative, a single-sided or double-sided flexible PCB may beused, e.g., having a thickness of about twenty five micrometer (25 μm).After assembly, the PCB may be folded, rolled, or otherwise arranged tominimize its volume.

[0114] To protect the sensor 12 and/or to prevent drift, the sensor 12may be covered with a protective coating, e.g., a moisture barrier (notshown). Preferably, the sensor 12 is coated with a relatively softmaterial, such as silicone (e.g., NuSil MED4161). This coating maysubstantially minimize the stiffness or stress that may be imposed uponthe sensor 12, which may otherwise affect its sensitivity and stability.Other protective and/or moisture barrier layers may then be applied overthis coating, such as a relatively thin metal layer and/or Parylene C,without significantly affecting performance of the sensor 12. After thesensor 12 is assembled and coated, it may be calibrated, for example, bytrimming the controller 18, e.g., by fuse blowing, and/or by solderingor otherwise bonding trim resistors 17 to the print side of the PCB 11.

[0115] The energy storage device 16, preferably a capacitor, may beattached to an edge of the PCB 11, e.g., bonded using epoxy or otheradhesive. Conductive glue may be used for electrical contacts. Theenergy transducer 14 is attached to the print side of the PCB 111, e.g.,by bonding with conductive glue. Additional mechanical fixation may beachieved, if desired, using an additional adhesive, such as an epoxy,around and/or under the energy transducer 14. Alternatively, the energytransducer 14 may be bonded using a conductive epoxy for electrical padareas, and a structural epoxy for areas away from the pads. When theenergy transducer 14 is attached to the PCB 11, the active area 15 ofthe energy transducer 14 is disposed away from the PCB 11 and/orotherwise exposed to transmit and/or receive acoustic energy, asdescribed further below.

[0116] Preferably, a panel of implants are assembled, e.g., by attachingthe components for multiple implants onto a single PCB. To calibrate thepanel (or individual implants) following assembly, the panel may beinserted into a testing and diagnostic chamber (not shown). The chambermay be thermostatically controlled to ensure substantially constanttemperature. In addition, pressure within the chamber may also becontrolled within pressure ranges defined by the implants'specifications, e.g., pressure ranges to which the implants may besubjected during use. Preferably, the chamber includes a “bed of nails”or similar fixture (also not shown) that provides contact betweendesired electrical pads on the PCB and the conductive “nails.” The nailsare coupled to external diagnostic electronics that may performdiagnostics and calibration, e.g., via trimming, as required. Thus, thediagnostic electronics may communicate and/or control the implants onthe panel via the nails. The testing generally includes calibration ofthe pressure sensors' sensitivity and offset, e.g., based uponcomparison of measurements of the implants to a calibrated pressuresensor, and/or calibration of the frequency of the internal oscillator.

[0117] Once the panel has been assembled and/or calibrated, the panelmay be separated into individual implants. For example, the panel may bediced using a milling machine, a dicing machine such as that used fordicing silicon wafers, a laser, or a knife-based cutter. If desired, anintermediate moisture barrier, such as Parylene C, may be applied to anyor all of the components, e.g., the pressure sensor, the controller,etc., to provide additional protection for the covered components.

[0118] After separation, each implant 10 is generally placed within abox or other casing (not shown). The casing may protect the implant 10from penetration of moisture or other body fluids, which may causecorrosion of the electrical pads or traces and/or may cause drift Thecasing may also provide mechanical protection and/or may provideconnection points from which to attach the implant 10, e.g., to otherdevices that may also be implanted within a patient. The casing may beprovided from titanium, gold, platinum, tantalum, stainless steel, orother metal. Alternatively, other biocompatible materials may be used,e.g., a polymer, such as a fluorocarbon, polyamide, PEEK, preferablycovered with a metallization layer to improve the polymer's performanceand/or to enhance its moisture resistance. The casing may also include aconnector or other attachment fixture that may facilitate connecting theimplant to other devices implanted within a patient's body, e.g., forreceiving a suture that extends from a stent-graft or other implanteddevice.

[0119] Preferably, the casing is a five-sided box, and the implant 10 isdisposed within the box such that the active areas of the sensor 12 andthe energy transducer 14 are exposed through the open side. The implant10 may be sealed within the box. For example, after assembly, a lid (notshown) may be attached to the sixth side, e.g., by welding, soldering,brazing, gluing, and the like. The lid may include openingscorresponding to the active areas of the sensor 12 and/or the energytransducer 14, the perimeters of which may be sealed. Alternatively, asix sided casing may be used, having one side made of a relatively thinfoil, e.g., only a few microns thick. In a further alternative, asix-sided compartment may be used, with one or more walls or one or moreregions of walls being thinner than the others. The interior of thecasing may be filled with a non-ionic solution, e.g., silicone oil,silicone gel, or other low modulus material, for coupling the pressuresensor and the energy transducer to the foil or thin-walled regions.U.S. Pat. No. 4,407,296 issued to Anderson, the disclosure of which isexpressly incorporated herein by reference, discloses a casing that maybe appropriate for use with an implant, in accordance with the presentinvention.

[0120] With the implant 10 within the casing, it may placed in a vacuumoven, e.g., at a temperature of about eighty degrees Celsius (80 C) foroutgassing, followed by plasma treatment for surface activation. Theimplant 10 may be attached to the casing using an adhesive, such as anepoxy, or silicone. The outer surface of the assembled casing andimplant may be covered with a layer of Parylene C for improvingcorrosion resistance, a polymer to improve biocompatibility, and/or ametal deposition layer to provide a final moisture barrier. Preferably,a metal coating may be applied, which may electrically ground the casingwith the energy transducer 14, and then a final coating of Parylene C orother corrosion resistance coating may be applied.

[0121] Turning to FIGS. 13A and 13B, in an alternative embodiment, animplant 53 may be assembled using wire bonding rather than the flip-chipprocess described above. Similar to the previous embodiment, the implant53 generally includes a sensor 55, one or more energy transducers 54,one or more energy storage devices 56, and a controller 58, which mayinclude any of the subsystems or components described above. The implant53 may be mounted within a casing (not shown), which may be formed fromTitanium or other material, similar to the previous embodiment. In theexemplary embodiment shown, the overall dimensions of the implant 53 maybe not more than about 5.75 mm long, 2.1 mm wide, and 0.95 mm deep. Thecasing may have a width about 0.1 mm wider than the widest component,e.g., the controller 58, and a depth of about 1.3 mm. Of course, thesedimensions are only exemplary and may be varied to accommodate differentsize components or to facilitate implantation within predeterminedlocations within a patient's body.

[0122] During assembly, the sensor 55, the energy storage device(s) 56,and the controller 58 may be attached to the casing, e.g., to a bottompanel 69 (shown in phantom in FIG. 13B). After fabricating the energytransducer(s) 54, e.g., using the methods described above, the energytransducer(s) 54 may be attached to the controller 58, e.g., to an uppersurface, as shown. The energy storage device(s) 56, e.g., one or morecapacitors, may be coated, e.g., to electrically isolate the positiveterminal and/or other portions of the energy storage device(s) 56.

[0123] Wires 59 may be bonded to provide any required electricalconnections between the components, e.g., between the sensor 55, theenergy exchanger(s) 54, the energy transducer(s) 56, and/or thecontroller 58. For example, the components may include one or moreelectrical contacts 61 to which ends of respective wires 59 may besoldered or otherwise bonded using known methods. The wires 59 may bebonded before testing the controller 58, e.g., in order to testoperation of the entire implant 53. Alternatively, the wires 59 may bebonded after testing the controller 58 and/or other componentsindividually or at intermediate stages of testing. For example, testing,calibration, and/or trimming the controller 58 may be completed using aprobe card (not shown) that may be coupled to leads on the controller58, e.g., similar to the bed of nails described above. During or aftertesting, trim resistor(s) 117 may be attached to the bottom 69 of thecasing and/or electrically coupled to the controller 58 or othercomponent. The trim resistor(s) 57 may be electrically isolated from theother components.

[0124] The subassembly may be cleaned and/or coated, similar to theprevious embodiment. For example, the entire subassembly may be coatedwith Parylene or other moisture barrier. The sensor may be coated, forexample, with silicone (NuSiI), which may still expose an active area ofthe sensor, e.g., a membrane of a pressure sensor, to body conditions.Ground connections may be made, e.g., for the trim resistors 57 and/orother components. The casing may then be at least partially filled withpotting compound, e.g., using a mold to protect the active area of thesensor 55. Preferably, the potting compound is filled to line 62 (shownin phantom in FIG. 13B), thereby covering all of the components, exceptthe active area of the sensor 55 and/or the active area of the energytransducer(s) 54.

[0125] A lid, membrane, or other seal (not shown) may be attached to thecasing to protect the implant 53 from an exterior of the casing, whilestill coupling the active areas of the sensor 55 and/or the energytransducer 54 to the exterior, similar to the previous embodiment. Thespace within the casing above the potting compound 62 may be filled witha fluid to acoustically couple and/or otherwise couple the active areasto the lid, membrane, or other seal. The lid may be attached first tothe energy transducer 54 and then may be secured across an open end ofthe casing and/or the lid may be welded to the casing open end using alaser, electron beam plasma, magnetic welding, or any other weldingmethod. The welding may be performed in a gas environment, preferably aninert gas (e.g., helium or argon), or while the parts are immersedwithin a fluid. Alternatively a thin membrane may be chemically etchedor diffusion bonded to the lid.

[0126] Wire bonding may have advantages over the flip-chip processdescribed above. For example, wire bonding may eliminate need for thePCB 11, and may allow the pressure sensor or other sensor to be mountedface up within the casing, which may simplify assembly. In addition,wire bonding may allow the implant 53 to be narrower in width and/orshorter in length than the previous embodiment. Because of theelimination of the PCB 11, the implant 53 may be easier, less expensive,and/or faster to assemble.

[0127] Turning to FIG. 14, during operation of an implant in accordancewith the present invention, such as the implant 10, e.g., uponimplantation within a patient's body 90, the implant 10 may beconfigured to operate in a “half-duplex” mode. In this mode, an externaltransducer 70 located outside the patient's body 90 may be used tocontrol, charge, and/or communicate with the implant 10. The externaltransducer 70 includes a probe 72 having one or more energy transducers74, e.g., similar to the energy transducer of the implant 10, forconverting energy between acoustic energy and electrical energy. Theexternal transducer 70 also generally includes control circuitry 76,memory for storing data 78, and a transmitting/receiving (T/R) switch80, which may be separate from, but coupled to, the probe 72, or may bewithin the probe (not shown). The T/R switch 80 may toggle the energytransducer 74 to operate in one of two modes, an energizing mode forcharging or activating the implant 10, and a receiving mode forreceiving data from the implant 10. As described below, the externaltransducer 70 may automatically switch between these two modes one ormultiple times during use.

[0128] First, the probe 72 may be coupled to the patient, e.g., placedagainst the patient's skin 92, and the energy transducer 74 operated inthe energizing mode, transmitting acoustic energy from its energytransducer to the implant 10 through the patient's body 90. The acousticenergy from this energizing transmission passes through the patient'sbody 90, at least some of the energy striking the active area 15 of theenergy transducer 14 of the implant 10. The energy transducer 14converts the acoustic energy into electrical energy, e.g., which may beused to charge the energy storage device (not shown) or otherwiseoperate the implant 10, and/or to receive commands from the externaltransducer 70, as explained further below.

[0129] Initially, the external transducer 70 may be operated in adiagnostic mode. For example, the external transducer 70 may transmit abroadband signal or a scanning signal, i.e., scanning through a range offrequencies, and wait for the implant 10 to respond. The implant 10 maytransmit at different frequencies in response to the diagnostic signal,and the external transducer 70 may determine the optimal frequency forcommunicating with the implant based upon the responses. For example,the external transducer 70 may repeatedly charge the implant 10 usingdifferent frequency signals and measure the length of time that theimplant 10 is capable of sampling and transmitting data signals at eachfrequency to determine the optimal frequency. Alternatively, when theimplant 10 detects the signal, it may transmit a response, the responsebeing at an optimal frequency that should be used to communicate withthe implant 10.

[0130] Once the external transducer 70 has determined the optimalfrequency for communicating with the implant 10 (or the externaltransducer 70 may already know the proper frequency to use), theexternal transducer 70 may then begin its operation in energizing mode,transmitting acoustic energy from its energy transducer 74 through thepatient's body 90 to the implant 10, which is stored in the energystorage device. The energy storage device may continue to store energyuntil a predetermined voltage is achieved, e.g., about eight Volts (8V), and then the controller (not shown) may automatically disconnect theenergy storage device from the energy transducer 14. Alternatively, theenergy storage device may continue to store energy until a stop commandis transmitted by the external transducer 70.

[0131] After a predetermined time, e.g., between about five and sixtyseconds (5-60 sec.), the external transducer 70 may automatically ceasethe energizing transmission. At the end of the energizing transmission,the external transducer 70 may send an identification code, e.g., apredetermined pulse sequence, identifying a specific implant. Inaddition, the external transducer 70 may send a stop command, anactivation command, a sampling rate instruction, or one or more otherinstructions. The external transducer 70 may then automatically switchto receiving mode and await data transmission from the implant 10matching the identification code. Alternatively, the external transducer70 may be switched manually to its receiving mode.

[0132] The controller of the implant 10 may detect the end of theenergizing transmission and the identification code. The controller mayconfirm that the identification code matches the implant 10, andautomatically activate the implant 10. Alternatively, the controller mayacquire an activation command or other instructions from the externaltransducer 70, such as a sampling rate and the like, and activate inaccordance with the instructions.

[0133] For example, once activated, the implant 10 may draw electricalenergy from the energy storage device, and begin to sample data usingthe sensor 12. The controller may receive signals, e.g., raw pressurereadings, from the sensor 12, digitize and/or otherwise process thesignals, and transmit sensor data using the energy transducer 14. Forexample, the A/D converter may convert the raw pressure readings intodigital data signals, which may be further processed by the controllerin preparation for data transmission. The energy transducer 14 mayconvert the processed digital data signals from the controller intoacoustic energy that may be transmitted through the patient's body 90 tothe external transducer 70.

[0134] The implant 10 may continue to sample data and transmit the datasignals until the voltage of the energy storage device 16 falls below apredetermined threshold, e.g., below a level at which the pressuresensor may not continue to operate effectively, such as 1.5 volts. Forexample, using a 4.7 μF tantalum capacitor for the energy storage device16, the implant 10 may operate for between about two and six seconds(2-6 sec.). After the voltage falls below the predetermined threshold,the controller may automatically discontinue operation of the implant 10and return to a passive state until energized and activated by theexternal transducer. The controller may also include additionalinformation in the data transmission, e.g., an initial confirmation ofinstructions received from the external transducer, an identificationcode identifying the implant 10, and/or a stop notice when the signaltransmission is being discontinued.

[0135] Thus, the external transducer 70 and one or more implants withinthe patient may operate in a cooperative manner. The external transducer70 may energize one or more implants with an energizing transmissionand/or may send instructions to individual or multiple implants. Thus,the external transducer 70 may selectively activate and receive datafrom one or more implants. The activated implant(s) may acquire data,transmit data signals to the external transducer 70 as acoustic energy,and then automatically return to their passive mode awaiting furtherinstructions. The external transducer 70 may receive data from the oneor more implants, which may be stored in memory 78 of the externaltransducer 70 or transferred to other equipment for use by medicalpersonnel and the like.

[0136] In an alternative embodiment, the energy storage device mayinclude a first relatively fast-charging capacitor and a secondrelatively slow-charging capacitor (not shown). For example, the firstcapacitor, which may be a relatively low-value capacitor, may be coupledto the energy transducer 14 initially, and, once the first capacitor ischarged, the second capacitor, which may be a much higher valuecapacitor, may then be coupled to the energy transducer 14. In addition,once the first capacitor is charged, the controller may automaticallytransmit a signal to the external transducer, thereby opening acommunication channel with the external transducer, e.g., identifyingthe implant 10, identifying its optimal communication frequency, and thelike.

[0137] For example, the first capacitor may charge in about fifty to twohundred milliseconds (50-200 ms), thereby allowing the implant torespond promptly upon detecting a signal from an external transducer,e.g., within about fifty to two hundred milliseconds (50-200 ms). Thecharge retained by the first capacitor, however, may only allow theimplant 10 to transmit a short reply, e.g., an identification code orother one or two word acknowledgement, in response to an interrogationfrom the external transducer. The second capacitor may retain a moresubstantial charge, e.g., that may be used to operate the implant 10 formore extended periods of time, similar to the embodiment describedabove.

[0138] In a further alternative embodiment, the external transducer 70and implant 10 may operate in a quasi-continuous state, i.e.,alternating between energizing/charging modes and transmitting/receivingmodes. For example, the external transducer 70 may transmit anenergizing transmission, e.g., for between about one and one hundredmilliseconds (1-100 msec.), to charge the energy storage device withsufficient energy to operate the implant 10 for a predetermined time,e.g., several milliseconds. The external transducer 70 may then switchto receiving mode, and the implant 10 may become activated, as describedabove, and sample and transmit data. After the predetermined time, theimplant 10 may automatically switch back to charging mode and wait foranother energizing transmission from the external transducer 70. Afterreceiving the data transmission from the implant 10, the externaltransducer 70 may switch back to the energizing mode and transmitanother energizing transmission to recharge the implant 10. Thus, theprocess of “interrogating,” i.e., requesting data from the implant 10,and transmitting sensor data may be repeated substantially indefinitely,as desired. For example, the external transducer 70 and implant 10 mayoperate at a predetermined duty cycle, e.g., at a rate of about fifteento thirty Hertz (15-30 Hz), depending upon how much information isneeded. This mode of operation may allow a smaller capacitor or otherenergy storage device to be used, while still allowing substantiallycontinuous monitoring with no specific duration limit.

[0139] This quasi-continuous mode may also be implemented by the implant10 in a hybrid mode. The external transducer 70 may transmit anenergizing signal whenever the operation of the implant 10 allows. Forexample, when the implant 10 is obtaining and/or processing data orbetween bits being transmitted by the implant 10, the energy transducer14 may be available to receive additional energy from the externaltransducer. These additional energizing signals may be used to “top off”the charge on the energy storage device, thereby substantially extendingthe length of time that the implant 10 may operate.

[0140] In a further alternative embodiment (not shown), the implant maybe operated in full-duplex mode. To facilitate this mode, the energytransducer is generally configured to transmit at a different frequencythan the data signal transmissions of the implant. This may be achievedby providing one or more separate energy transmitters and receivers inthe external transducer. Alternatively, the external transducer mayinclude a single energy transducer and a circuit for separating the datatransmission frequency, similar to the transmission circuit shown inFIG. 12 and described above. Thus, the external transducer and theimplant may both be configured for filtering and/or otherwise separatingthe two transmissions from one another. Full-duplex mode may allow theimplant truly to operate continuously. Because the energy transducer ofthe implant may receive energy substantially continuously from theexternal transducer via the energizing transmission, the implant maysample and transmit data substantially indefinitely, if desired, oruntil a stop command is transmitted from the external transducer.

[0141] Although full-duplex mode allows continuous operation of theimplant, the half-duplex mode also has advantages over the full-duplexmode. First, because of its higher efficiency, i.e., only activatingcomponents as they are needed, half-duplex mode may reduce the amount ofenergy consumed by the implant 10, allowing the implant 10 to operate athigher voltages, although for relatively short periods of time. Second,simultaneous energizing and transmitting in full-duplex mode may causeinterference between the energizing and data signal transmissions. Inparticular, because the energizing transmission is much stronger thanthe data signal transmission, the energizing transmission may createbackground noise for the signal transmission. In half-duplex mode, theenergizing and data signal transmissions are separated in time,increasing the fidelity and detection of the signal transmission.Finally, half-duplex mode may allow a single energy transducer to beused as both an energy exchanger and as a transmitter, simplifyingconstruction of the implant and possibly reducing the amount of acousticenergy needed.

[0142] Having described various embodiments of an implantable biosensorand systems for communicating with implantable biosensors, barometricpressure correction for implantable devices will now be described. Themethods and systems described herein can be used with any implantable orexternal device that can benefit from barometric pressure data orbarometric pressure correction. In particular, we will describe themethods and systems as they are used in connection with an implantablebiosensor or implantable patient monitor. But in addition to implantablebiosensors and implantable patient monitors, the present systems andmethods can also be used in conjunction with other implantable andexternal devices, such as pacemakers, ventricular assist blood pumps,implantable and external drug delivery pumps such as insulin pumps,infusion pumps, artificial hearts, lung machines, drug infusion and drugrelease devices activated with telemetric signals, defibrillators,neurostimulating devices, aortic assistant balloons, intra ocular shuntsfor controlling intra ocular pressure, intra cranial shunts,incontinence control devices, contrast media automatic injectors,impotence devices, etc.

[0143]FIG. 15A shows a system for measuring pressure in a body byconverting absolute pressure data acquired from an implantable biosensorto gauge pressure data. The system includes an implantable biosensor700. The implantable biosensor 700 can be of any type, including thoseshown and described in FIGS. 1A-14. The implantable biosensor 700 isconfigured to obtain absolute pressure data within an anatomicalstructure, such as a blood vessel. The implantable biosensor 700 caninclude a pressure sensor and an internal controller coupled to thepressure sensor for acquiring absolute pressure data from the pressuresensor. The implantable biosensor 700 can also include an acoustictransducer for converting energy between electrical energy and acousticenergy. The acoustic transducer of the biosensor 700 can be configuredto convert acoustic energy from an external monitor 800 into electricalenergy to power the biosensor 700. The acoustic transducer of thebiosensor 700 can include an acoustic transmitter for transmitting anacoustic signal to the external monitor 800. More particularly, it canbe configured to transmit an acoustic signal comprising absolutepressure data to the external monitor 800. In addition, the acoustictransducer can include an energy exchanger coupled to an energy storagedevice. The energy storage device can be configured for storingelectrical energy converted by the acoustic transducer from acousticenergy. In one embodiment, the biosensor 700 can include a processor forcalculating gauge pressure based on the absolute pressure that itmonitors and measures and barometric pressure information received fromthe external monitor 800. The biosensor 700 can transmit the pressuredata, whether it be absolute pressure or gauge pressure to the externalmonitor using a telemetric signal.

[0144] The system shown in FIG. 15A can also include an external monitor800, a GPS satellite communications system 920, a computer system ornetwork 900, and a database 910 in communication with or stored in amemory of the computer system 900. The database 910 can includereal-time barometric pressure data for numerous geographic locationsthroughout the world. The database 910 can alternatively be associatedwith a remote computer system, which can be accessed by the computersystem 900, or directly by the external monitor 800 through atelecommunications link achieved through a wireless transmitter 850 orconnector or lead (not shown) extending from the external monitor 800.

[0145] The external monitor 800 can be like any one of those externalcommunications devices shown and described in FIGS. 1A-14 particularlyFIGS. 3, 4, and 14. The external monitor 800 can be configured toreceive absolute pressure data from the biosensor 700, real-timebarometric pressure data from the database 910, or gauge pressure datacalculated by the computer system 900 or other source. In addition, itcan be configured to receive barometric pressure data from a barometer885 (shown in FIG. 15B), through a lead or connector, or throughwireless transmission of data through the wireless transmitter 850.Alternatively, the barometer 885 can be integrated into the externalmonitor 800 (not shown).

[0146] Preferably, the external monitor 800 includes a centralprocessing unit or microprocessor 810. The microprocessor 810 can beconfigured to control an acoustic transducer 840, with which it is incommunication. The external monitor 800 can include an energy source 855for powering the external monitor 800, and particularly the acoustictransducer 840. The acoustic transducer 840 can be configured to convertacoustic signals received from the biosensor 700, which can representinter alia absolute pressure data, into electrical signals. The acoustictransducer can transmit the electrical signals to the microprocessor 810for processing and storage within a memory 830. Like the memory 424described in relation to FIG. 4, the memory 830 may be a temporarybuffer that holds data before transfer to another device, ornon-volatile memory capable of storing the data substantiallyindefinitely, e.g., until extracted by the microprocessor 810 or otherelectronic device. The memory can be configured to store geographiclocation data, altitude data, temporal data, and pressure data.

[0147] The microprocessor 810 can also include a computer program, suchas an Internet browser, which is configured for interfacing with thecomputer system 900, a global communications network, or an outsideelectronic device (not shown). The microprocessor can also include acomputer program 870 configured to calculate gauge pressure data bysubtracting barometric pressure data from absolute pressure data basedon the following equation:

Pgauge=Pabs−Pbaro

[0148] where

[0149] Pgauge=gauge pressure

[0150] Pabs=absolute pressure

[0151] Pbaro=barometric pressure

[0152] The computer program 870 can also be configured to factor inaltitude, which changes barometric pressure by about 1 mbar per everyeight meters in altitude based on the following equation:

P(z)=P(sea level)^(−z/H)

[0153] where

[0154] P(z)=pressure at height z

[0155] P(sea level)=seal level pressure (˜1013 millibars)

[0156] z=height in meters

[0157] H=scale height (i.e., RT/g)

[0158] Alternatively, the computer program 870 can be associated with aprocessor located in the biosensor 700. The external monitor 800 canalso include an interface 820, which can include a keyboard or keypad.The interface 820 can also include a display for displaying pressuredata, including absolute pressure data received from the biosensor 700,barometric pressure data received from the computer system 900, database910, or barometer 885, or gauge pressure data.

[0159] The external monitor 800 can also include a GPS receiver 860 andan altimeter 880. Both the GPS receiver 860 and altimeter 880 can becoupled to or otherwise in communication with the microprocessor 810.The microprocessor 810 can be configured to process geographic locationdata and altitude data received from the GPS receiver 860 and altimeter880. Both the geographic location data and altitude data can be storedin the memory 830. Alternatively, the GPS receiver 860 and satellitesystem 920 can be used to provide altitude data in addition to or inconjunction with geographic position data, in which case the altimeter880 is unnecessary or can be integrated for redundancy.

[0160] The computer system 900 can be a personal computer, a local areanetwork, a wide area network, or any other system, including one thatincludes an Internet connection. The database 910 can be one storedwithin a memory directly associated with the computer system 900 andconstantly updated through manual input or automated retrieval ofinformation through satellite or telecommunications links with externalsources. The computer system 900 in turn can include a memory programmedwith the location and altitude data associated with its temporary orpermanent location and altitude. This data can be modified and thecomputer reprogrammed with new data whenever the computer system 900 ismoved to a new location. Alternatively, the database 910 can be a remotedatabase accessed by the computer system 900 through a globalcommunications network The external monitor 800 can be connected to thecomputer system 900 through a wireless communications link achievedthrough the wireless transmitter 850, or through a lead or connector(not shown). Wireless communication between the components of thesystem, such as the external monitor 800 and computer system 900, may beaccomplished or assisted using devices which conform to the BLUETOOTHstandard, a 2.4 GHz wireless technology employed to transport databetween cellular phones, notebook PCS, and other handheld or portableelectronic gear at speeds of up to 1 megabit per second. Other suitablewireless communication standards and methods now existing or laterdeveloped are contemplated in the present invention.

[0161] In another alternative, if the database 910 is a remote database,the external monitor 800 can communicate with the remote database 910through a telecommunications link 925 (shown in FIG. 15B) of its ownrather than through the computer system 900. This can be achieved by theuse of a mobile telephone or other electronic device (not shown)configured for wireless Internet access. The mobile telephone or otherelectronic device can be in communication with the external monitor 800through the wireless transmitter 850 or a lead or connector (not shown).Alternatively, the link with the remote database 910 can be achievedthrough telecommunications hardware and software (not shown) built intothe external monitor 800.

[0162] Now turning to FIG. 16, the external monitor 800 can receiveabsolute pressure data 1100 from the implantable biosensor 700 and canstore it in memory 830. The external monitor 800 can obtainlocation/altitude data 1000 from a number of sources as described inmore detail below, and can store that data in memory as well. Thelocation and altitude data 1000 and the absolute pressure data 1100 canall be transmitted through a download to a computer system 900, whichcan be a home unit. The computer system 900 can be used to obtainreal-time barometric pressure data from the remote database 910. Theremote database 910, can be associated with an Internet weather website, such as Yahoo® weather, Weather.com, or AWS.com, or it can be anydatabase that includes real-time barometric pressure data for numerouslocations throughout the world. The real-time barometric pressure datathat the computer system 900 retrieves from the remote database 910 cancorrespond with the location of the external monitor 800 as representedby the location data 1000. The computer system 900 can include analgorithm to calculate gauge pressure based on the following twoequations:

Pgauge=Pabs−Pbaro and P(z)=P(sea level)^(−z/H).

[0163] After calculating the gauge pressure including the altitudefactor, the computer system 900 can trasmit the gauge pressure data tothe external monitor 800, where the data can be displayed on theinterface 820, or it can be stored for subsequent retrieval in memory830. The computer system 900 can display the resulting gauge pressuredata on its computer screen simultaneously with or in place ofdisplaying it on the interface 820. The data can also be stored forsubsequent retrieval in a memory of the computer system 900.Alternatively, the computer system 900 can transmit real-time barometricpressure data corresponding to the geographic location associated withthe location data 1000 to the external monitor 800, which can thencalculate gauge pressure by using the computer program 870, which canuse an algorithm based on the same two equations shown above. The gaugepressure data can then be displayed on the interface 820, and it canalso be stored indefinitely in the memory 830 for subsequent recall. Inaddition, the computer system 900 can be preprogrammed withpredetermined location and altitude data. The external monitor 800 canthen be used to call upon the computer system 900 to obtain real-timebarometric pressure data from outside sources corresponding with thepredetermined location associated with the predetermined location data.

[0164] Alternatively, as shown in FIG. 17, the external monitor 800 cancommunicate directly with a remote database 910 having barometricpressure data. Again, the remote database 910 can be associated with anInternet weather web site, such as Yahoo® weather, Weather.com, orAWS.com, or it can be any database that includes real-time barometricpressure data for numerous locations throughout the world. Tocommunicate with the remote database 910, the external monitor 800 canbe coupled to a mobile telephone or other electronic device configuredfor wireless Internet access or access to the remote database 910. Theexternal monitor 800 can also include the requisite hardware andsoftware for wireless Internet access or wireless communication with theremote database 910, thus obviating the need for a mobile telephone orother external electronic device. Once in communication with the remotedatabase 910, the external connector can send its location data 1000 tothe database 910 and can request barometric pressure data for a locationcorresponding with the location represented by the location data 1000.The barometric pressure data is then received into the memory 830,whereupon the computer program 870 calculates gauge pressure data basedupon the same two equations shown above. The resulting gauge pressuredata can be displayed on the interface 826 and can be storedindefinitely in the memory 830 for subsequent recall. In addition, thelocation data 1000, absolute pressure data 1100, barometric pressuredata, gauge pressure data, and altitude data can all be stored in thememory 830 separately, and they can be transmitted, either through atelecommunications link or a lead or connector, to a home unit 930 forpermanent storage and subsequent recall. Alternatively, the home unit930 can transmit the data to a database 950 for permanent storage andsubsequent recall. The home unit 930 can be located at a facilitycontrolled and/or monitored by, for example, a healthcare organizationor doctor's office. Thus, the system enables rapid communication ofpressure data, as well as any physiological parameters monitored by thebiosensor 700, can be rapidly and automatically relayed to a doctor'soffice, which can store the information or use it for rapid deploymentof emergency healthcare services to the patient.

[0165] The location data 1000, can be determined in a number of ways. Inone embodiment, the GPS receiver 860 can obtain location data 1000 froma GPS satellite communications system 920. The GPS receiver can transmitthe data to the microprocessor 810, which can process the data and storeit in the memory 830. The GPS receiver 860 and GPS satellitecommunications system 920 can also determine altitude along withgeographic location for a packet of position data corresponding withgeographic position and altitude position.

[0166] Alternatively, the location data can be determined by the use ofa zip code or telephone number along with altitude data acquired by analtimeter 840. The microprocessor 810 can include a database of zipcodes and telephone number area codes and prefixes. The zip code ortelephone number can be entered through a keypad associated with theinterface 820 of the external monitor 800. The information can betransmitted to the microprocessor 810, which can process the informationand obtain location data 1000 and then store it in the memory 830.Alternatively, the external monitor 800 can obtain location data 1000 bycommunicating-by any of the means described above-with a remote database(not shown) of zip codes or telephone numbers with associated locationdata. It can send a request for location data associated with the zipcode or telephone number entered into the keypad, and it can receive thecorresponding location data 1000, which it can then process and store inthe memory 830. In yet another alternative, either of the computersystems 900 or 930 can include a database of zip codes or telephonenumbers with associated location data. The external monitor 800 cantransmit the zip code or telephone number to the computer system 900 or930 and receive the corresponding location data 1000. In yet anotheralternative, a mobile telephone network system can be used to obtainlocation data. The external monitor 800 can be coupled to a mobiletelephone (not shown), and can use the network associated with thatmobile phone to obtain location data 1000. In another alternative,location data can be obtained by using a local network location system.With this embodiment, precise gauge pressure data can be calculatedusing the altitude data from the altimeter 840 factored into thegeographic position data obtained using phone numbers, zip codes, mobiletelephone network systems, or local network location system.

[0167]FIG. 18A shows another embodiment of the invention. In thisembodiment, the external monitor 800 includes a barometer 980.Alternatively, the barometer 980 can be an external device that iscoupled to the external monitor 800 with a lead or connector or is inclose-range wireless communication with the external monitor 800. Thebarometer 980 can be calibrated using a remote database 910 havingreal-time barometric pressure data for numerous locations throughout theworld. The external monitor 800 can obtain accurate barometric pressuredata in any of the ways described with respect to FIGS. 16 and 17, whichcan include the use of a home unit 900.

[0168] For example, in one embodiment as shown in FIG. 18B, the systemcan include a computer system 900 that is preprogrammed with geographiclocation and altitude data, which corresponds with its home location.This data can be modified whenever the computer system 900 is moved to anew location. The external monitor 800 can call upon the computer system900 to retrieve real-time barometric pressure data from a remotedatabase 910, such as any of those described above. The computer system900 can then transmit that data to the microprocessor 810 of theexternal monitor 800, which can in turn transmit the data to thebarometer for processing and automated calibration of the barometer.Alternatively (not shown), the microprocessor 810 can store barometricpressure data received from the barometer 980 in the memory 830. Using acalibration algorithm, the microprocessor 810 can use the data receivedfrom the remote database 910 to correct the data from the barometer 980.The location and altitude data can be obtained in the same ways asdescribed with respect to FIGS. 16-18B.

[0169]FIG. 19 shows an embodiment of a method of correcting absolutepressure data received from an implantable biosensor to account forambient (e.g., barometric) pressure. The method utilizes an externalmonitor 800, such as that described above, which is capable ofperforming the steps involved in the method. The method includes thefirst step of using the external monitor 800 to receive a signal 1500from a biosensor 700. The signal can be any telemetric signal such asacoustic, RF, electromagnetic, microwave, light (e.g., infrared) or anyother form of telemetric signal. The signal can represent absolutepressure data. The next step can be to convert the signal into absolutepressure data 1510, which can be stored 1520 in a memory 830. This stepcan be accomplished with a transducer, such as the acoustic transducer840 described above, for converting the telemetric signal into anelectric signal, optical signal, or any other signal that can betransmitted to a microprocessor 810 of the external monitor 800. Themicroprocessor 810 can then process and store 1520 the absolute pressuredata in a memory 830.

[0170] In parallel fashion, the external monitor 800 can receiveposition data 1600 from various sources. The position data is then usedto obtain real-time barometric pressure data corresponding with thegeographic location represented by the position data. The steps ofobtaining the appropriate real-time barometric pressure data from aremote microprocessor are performed at steps 1530, 1610, 1620, and 1630.In one embodiment, the external monitor 800 includes a GPS receiver 860.The GPS receiver can receive GPS signals 1540 from GPS satellites 920,and it can process geographic position and altitude data 1550, thusdetermining the location and altitude of the external monitor 800 andconsequently the biosensor, which is in close proximity to the externalmonitor 800. Altitude data be obtained 1595 from an altimeter inaddition to or in place of the GPS system, the altimeter beingintegrated with or otherwise coupled to the external monitor 800.Alternatively, the geographic position of the external monitor 800 canbe determined using a local network location system 1560. In yet anotheralternative embodiment, the position of the external monitor 800 can bedetermined by using a mobile telephone network location system 1580.Alternatively, the position of the external monitor 800 can bedetermined by entering a phone number 1570 or a zip code 1590 into aninterface 820 keypad located on the external monitor 800. Themicroprocessor 810 of the external monitor 800 can either process theappropriate position data associated with the phone number or zip codeby searching an internal database of phone numbers and/or zip codes withcorresponding geographic position data. Alternatively, upon receivingposition data 1600, the microprocessor 810 can store it 1520 in aretrievable database, or it can send the position data to a remotemicroprocessor 1530 for use in retrieving relevant barometric pressuredata 1610. If the geographic position data represents a telephone numberor zip code rather than geographic position data, the remotemicroprocessor 810 can search its own database of phone numbers and zipcodes for corresponding geographic location data. Alternatively, it cansearch an online database of telephone numbers and zip codes forcorresponding geographic position data. The geographic position data isused by the remote microprocessor to select barometric pressure datacorresponding with the geographic location represented by the geographicposition data. Thus, the remote microprocessor searches a database ofreal-time barometric pressure data 1620, retrieves the appropriate data1610, and sends it to the microprocessor 810 of the external monitor1630, which consequently receives that data. The microprocessor 810 ofthe external monitor 800 can include an algorithm for calculating gaugepressure from absolute pressure using barometric pressure and altitudedata. The calculation involves the following equations:

Pgauge=Pabs−Pbaro and P(z)=P(sea level)^(−z/H)

[0171] Thus, the microprocessor 810 recalls the absolute pressure valuecorresponding with the absolute p ressure data and subtracts thebarometric pressure value associated with the real-time barometricpressure data received 1630 from the remote microprocessor, to calculategauge pressure 1640, which can be corrected for altitude based on thesecond equation. The final step is to display the gauge pressure 1650 onthe interface 820 of the external monitor 800.

[0172] In an alternative embodiment (not shown) the gauge pressurecalculation can be performed by an algorithm associated with the remotemicroprocessor rather than the microprocessor of the external monitor800. In addition, the gauge pressure can be displayed 1650 on a monitoror other interface of an outside electronic device or computer. Theelectronic device or computer can either be coupled to the externalmonitor 800 through leads or connectors, or can otherwise communicatewith the external monitor 800 through short-range telemetry, such as RF,microwave, acoustic, electromagnetic, light (e.g., infrared), etc.

[0173]FIG. 20 shows another embodiment of a method of correctingabsolute pressure data received from an implantable biosensor, such asthe biosensor 700 described above, to account for ambient (e.g.,barometric) pressure. The method again utilizes an external monitor,such as the external monitor 800 described above, which is capable ofperforming the steps involved in the method. The method also utilizes abarometer 885. The barometer 885 can be integrated into the externalmonitor 800 and directly communicating with the microprocessor 810 ofthe external monitor 800. Alternatively, the barometer 885 can be astand-alone device that is coupled to the external monitor 800 withleads or connectors or in communication with the external monitor 800through short-range telemetry, such as RF, microwave, acoustic,electromagnetic, light (e.g., infrared), etc therewith.

[0174] The method includes the first step of using the external monitor800 to receive a signal 2000 from a biosensor 700. The signal can be anytelemetric signal such as acoustic, RF, electromagnetic, microwave,light (e.g., infrared) or any other form of telemetric signal. Thesignal can represent absolute pressure data. The next step can be toconvert the signal into absolute pressure data 2010, which can be stored2020 in a memory 830. This step can be accomplished with a transducer,such as the acoustic transducer 840 described above, for converting thetelemetric signal into an electric signal, optical signal, or any othersignal that can be transmitted to the microprocessor 810 of the externalmonitor 800. The microprocessor 810 can then process and store 2020 theabsolute pressure data in a memory 830.

[0175] In parallel fashion, the external monitor 800 can receiveposition data 2100 from various sources. The position data can includealtitude data as well. The position data is then used to obtainreal-time barometric pressure data corresponding with the geographiclocation represented by the position data. The steps of obtaining theappropriate real-time barometric pressure data from a remotemicroprocessor are performed at steps 2030, 2110, 2120, and 2130. In oneembodiment, the external monitor 800 includes a GPS receiver 860. TheGPS receiver 860 can receive GPS signals 2040 from GPS satellites 920,and it can process geographic position data (including altitude data)2050, thus determining the location of the external monitor 800 andconsequently the biosensor 700, which is in close proximity to theexternal monitor 800. Alternatively, the geographic position of theexternal monitor 800 can be determined using a local network locationsystem 2060. In yet another alternative embodiment, the position of theexternal monitor 800 can be determined by using a mobile telephonenetwork location system 2080. Alternatively, the position of theexternal monitor 800 can be determined by entering a phone number 2070or a zip code 2090 into an interface 820 keypad located on the externalmonitor 800. The microprocessor 810 of the external monitor 800 caneither process the appropriate position data associated with the phonenumber or zip code by searching an internal database of phone numbersand/or zip codes with corresponding geographic position data.Alternatively, upon receiving position data 2100, the microprocessor 810can store it 2020 in a retrievable database or memory 830, or it cansend the position data to a remote microprocessor 2030 for use inretrieving relevant barometric pressure data 2110. If the geographicposition data represents a telephone number or zip code rather thangeographic position data, the remote microprocessor 810 can search itsown database of phone numbers and zip codes for corresponding geographiclocation data. Alternatively, it can search an online database oftelephone numbers and zip codes for corresponding geographic positiondata. The geographic position data is used by the remote microprocessorto select barometric pressure data corresponding with the geographiclocation represented by the geographic position data. Thus, the remotemicroprocessor searches a database of real-time barometric pressure data2120, retrieves the appropriate data 2110, and sends it 2130 to themicroprocessor 810 of the external monitor 800, which consequentlyreceives that data. The real-time barometric pressure data is then usedto calibrate 2140 the barometer 885. The calibration can be performedmanually or automatically. In the case of automated calibration, thereal-time barometric pressure data can be transmitted to the barometer,where a calibration algorithm associated with the barometer 885microprocessor performs the calibration.

[0176] In another embodiment (not shown), the microprocessor 810 of theexternal monitor 800 can save and recall the barometric pressure datareceived from the barometer 885 and can calibrate that data based on thereal-time barometric pressure data received from the remotemicroprocessor at step 2130. Thus, the calibration is performed by themicroprocessor of the external monitor 800 rather than the barometer.

[0177] In addition, in the same manner as described with respect to theembodiment shown in FIG. 19, the microprocessor 810 of the externalmonitor 800 can include an algorithm 870 for calculating gauge pressurefrom absolute pressure using barometric pressure. The calculationinvolves subtracting the barometric pressure value from the absolutepressure value. Thus, the microprocessor 810 recalls the absolutepressure value corresponding with the absolute pressure data andsubtracts the barometric pressure value obtained by the calibratedbarometer 885, to calculate gauge pressure 2150. The final step is todisplay the gauge pressure 2160 on the interface 820 display on theexternal monitor 800 or the barometer 885.

[0178] In an alternative embodiment (not shown) the gauge pressurecalculation can be performed by an algorithm associated with the remotemicroprocessor rather than the microprocessor 810 of the externalmonitor 800. In addition, the gauge pressure can be displayed 2160 on amonitor or other interface of an outside electronic device or computer.The electronic device or computer can either be coupled to the externalmonitor 800 through leads or connectors, or can otherwise communicatewith the external monitor 800 through short-range telemetry, such as RF,microwave, acoustic, electromagnetic, light (e.g., infrared), etc.

[0179] As shown in FIG. 21, in which like numbers have been used to showlike components with respect to the previous figures, the presentsystems and methods can also be used to provide barometric pressureinformation to any meddical apparatus such as pacemakers, ventricularassist blood pumps, implantable and external drug delivery pumps such asinsulin pumps, infusion pumps, artificial hearts, lung machines, druginfusion and drug release devices activated with telemetric signals,defibrillators, neurostimulating devices, aortic assistant balloons,intra ocular shunts for controlling intra ocular pressure, intra cranialshunts, incontinence control devices, contrast media automaticinjectors, impotence devices, etc. A medical device 3000 is shown, whichis modified to communicate with the external monitor 800, a computersystem 900 or a remote source 910. The medical device 3000, for examplean external insulin pump, which delivers insulin to the patient throughan infusion set 3250 inserted under the skin of the patient. The device3000 can include an interface 820, a micrprocessor 810 for controllingthe pump, a GPS receiver 860 to communicate with a GPS satellite system920 for determining the location of the pump, a memory 830, and antenna850 for wireless communication with outside and/or remote sources. Thedevice 3000 can include built in telecommunications hardware andsoftware in a telecommunications module 3100 for communicating with acomputer system 900 or a remote source of information 910, such as a website. The computer system 900 or the remote source 910 can includereal-time barometric pressure information for a plurality of geographiclocations. Alternatively, the device 3000 can communicate with anexternal monitor 800, which can relay information from a computer system900 or a remote source 910 to the device 3000.

[0180] It will be appreciated that the above descriptions are intendedonly to serve as examples, and that many other embodiments are possiblewithin the spirit and the scope of the present invention.

What is claimed is:
 1. A system for measuring pressure in a body,comprising: an implant device configured for measuring absolute pressurein a body, the implant device further configured to communicate measuredabsolute pressure information outside of the body using telemetricsignals; and an external monitor configured to receive telemetricsignals from the implant device, receive barometric pressure informationfrom a remote source, the barometric pressure information associatedwith a geographic location of the body, and derive gauge pressure fromthe received absolute pressure information and barometric pressureinformation.
 2. The system of claim 1, wherein the telemetric signalsare acoustic signals.
 3. The system of claim 1, wherein the telemetricsignals are radio frequency signals.
 4. The system of claim 1, whereinthe remote source comprises real-time barometric pressure informationfor a plurality of geographic locations.
 5. The system of claim 1,further comprising a global positioning system (GPS) signal receivercoupled to at least one of the external monitor and the implant device.6. The system of claim 5, wherein the external monitor is configured toreceive position information from the GPS signal receiver andcommunicate the position information to the remote source, and whereinthe received barometric pressure information corresponds to the positioninformation.
 7. A system for measuring pressure in a body, comprising:an implant device configured for measuring absolute pressure in a body,the implant device further configured to communicate measured absolutepressure information outside of the body using telemetric signals; andan external monitor configured to receive telemetric signals comprisingabsolute pressure information from the implant device, transmit receivedabsolute pressure information to a remote source, the remote sourcecomprising real-time barometric pressure information corresponding witha location of the body, and receive gauge pressure information from theremote source, the gauge pressure information derived from the absolutepressure information and barometric pressure information.
 8. The systemof claim 7, wherein the remote source comprises real-time barometricpressure information for a plurality of geographic locations.
 9. Asystem for measuring pressure in a body, comprising: an external monitorconfigured to receive barometric pressure information from a remotesource, the barometric pressure information associated with a geographiclocation of the body; and an implant device configured to receivebarometric pressure information from the external monitor, measureabsolute pressure in a body, and derive gauge pressure from the receivedabsolute pressure information and measured barometric pressureinformation.
 10. The system of claim 9, wherein the remote sourcecomprises real-time barometric pressure information for a plurality ofgeographic locations.
 11. A method for measuring pressure in a body,comprising: receiving a telemetric signal from a biosensor implanted ina body, the telemetric signal representing absolute pressureinformation; receiving real-time barometric pressure information from aremote source, the real-time barometric pressure informationcorresponding to a geographic location of the body; and deriving gaugepressure from the absolute pressure information and barometric pressureinformation
 12. The method of claim 11, wherein the geographic locationof the body is determined using a GPS receiver.
 13. The method of claim11, wherein the geographic location of the body is determined based on apostal code.
 14. The method of claim 11, wherein the geographic locationof the body is determined based on a telephone number.
 15. The method ofclaim 11, wherein the gauge pressure is derived by an external monitorproximate the body.
 16. The method of claim 11, wherein the gaugepressure is derived by the implanted biosensor.
 17. The method of claim11, wherein the gauge pressure is derived by the remote source.
 18. Themethod of claim 11, wherein the remote source comprises a web sitecomprising weather information.
 19. The method of claim 11, furthercomprising displaying the gauge pressure value on a display proximatethe body.
 20. A method for measuring pressure in a body, comprising:receiving a signal from a biosensor implanted in a body; derivingabsolute pressure information from the signal; and receiving real-timebarometric pressure information associated with a geographic location ofthe biosensor from a remote source.
 21. The method of claim 20, furthercomprising calibrating a barometer according to the real-time barometricpressure information, the barometer in communication with an externalmonitor proximate the body; using the calibrated barometer to determinean ambient pressure; and deriving a gauge pressure based on the ambientpressure and absolute pressure information.
 22. A system for measuringpressure in a body, comprising; an implant device for measuringintra-body absolute pressure, the implant device comprising a pressuresensor, and a transducer coupled to the pressure sensor for acquiringabsolute pressure information from the pressure sensor, the transducerconfigured to transmit acoustic signals comprising absolute pressureinformation acquired from the pressure sensor; an external monitorconfigured to receive acoustic signals from the implant device and toreceive real-time barometric pressure information from a remote source,the remote source comprising real-time barometric pressure informationfor more than one geographic location; and a global positioning system(GPS) signal receiver coupled to the external monitor, the externalmonitor further configured to derive gauge pressure based on absolutepressure information received from the implant device and real-timebarometric pressure received from the remote source.
 23. The system ofclaim 22, wherein the remote source comprises a web site comprisingweather information.
 24. A method for measuring pressure in a body,comprising: receiving an acoustic signal from a biosensor implanted inthe body; deriving absolute pressure information from the acousticsignal; establishing a communications link with a remote sourcecomprising real-time barometric pressure information for more than onegeographic location; through the communications link, receivingreal-time barometric pressure information from the remote source;deriving gauge pressure by subtracting a pressure value correspondingwith the real-time barometric pressure information from a pressure valuecorresponding with the absolute pressure information; and displayingsaid gauge pressure on a display.
 25. The method of claim 24, furthercomprising determining a respective geographic location and altitude ofthe bionsensor using a GPS receiver, wherein the real-time barometricpressure information from the remote source corresponds with thegeographic location determined by the GPS receiver.
 26. The method ofclaim 24, wherein the remote source is associated with a web sitecomprising weather information.
 27. A method for communicating with adevice implanted in a body, comprising: receiving a telemetric signalfrom the device, the telemetric signal representing absolute pressureinformation; receiving real-time barometric pressure information from aremote source, the real-time barometric pressure informationcorresponding to a geographic location of the body; and deriving gaugepressure from the absolute pressure information and barometric pressureinformation.
 28. The method of claim 27, wherein the device is abiosensor.
 29. The method of claim 27, wherein the device is a druginfusion pump.
 30. The method of claim 27, wherein the remote sourcecomprises a web site comprising weather information.
 31. A method forproviding barometric pressure information to a medical devicecomprising: determining the geographic location of the medical device;and receiving real-time barometric pressure information from a remotesource, said remote source comprising real-time barometric pressureinformation for a plurality of geographic locations, the real-timebarometric pressure information corresponding to a geographic locationof the medical device.